Under the Foreign Acquisitions and Takeovers Act 1975, certain 'significant actions' can be prohibited by the Treasury if considered to be contrary to the 'national interest'. These include actions to acquire interests in securities, assets or Australian land, and actions taken in relation to entities (being corporations and unit trusts) and businesses, that have a connection to Australia. In general, a change in control and meeting a monetary threshold test are required for an action to be significant. The national interest, and what would be contrary to it, is not defined in the Act or the Foreign Acquisitions and Takeovers Regulation 2015. Assessments are made on a case-by-case basis. However, a Foreign Investment Policy document states that the Government typically considers the following factors when assessing foreign investment proposals: national security; competition; other Australian government policies, including tax; impact on the economy and the community and the character of the investor.
Additionally, any 'notifiable action' must be notified to the Treasury before the action can be taken. A notifiable action is a proposed action by a foreign person to acquire a direct interest in an Australian entity or Australian business that is an agribusiness, to acquire a substantial interest (generally at least 20%) in an Australian entity or to acquire an interest in Australian land. Generally, the action is notifiable when a monetary threshold test is met. The monetary screening thresholds concern either the amount paid for an interest or the value of an entity or assets. The relevant threshold depends on the type of investor and type of action taken. Generally, a higher threshold applies for investors from certain countries with which Australia has free trade agreements when these investors invest in non-sensitive businesses. Sensitive businesses, as defined in the Regulation, include transport, media and telecommunications businesses, among others. 
Certain acquisitions are exempted from reviews by virtue of the 2015 Regulation. Generally, acquisitions by foreign non-government acquirers of an Australian business carried on by, or an acquisition of an interest in Australian land from the Commonwealth, a State, a Territory or a local governing body of Australia or an entity wholly owned by the Commonwealth, a State, a Territory or a local governing body, are exempted from reviews. However, acquisitions of an interest in Australian land if the interest is, or includes, certain infrastructure assets, are excluded from the exemption. These infrastructure assets include 'public infrastructure', which is defined in the Regulation as including also electricity generation, transmission, distribution and supply systems and facilities.
"4 Dictionary of definitions
In this Act: [...]
foreign person means:
(a) an individual not ordinarily resident in Australia; or
(b) a corporation in which an individual not ordinarily resident in Australia, a foreign corporation or a foreign government holds a substantial interest; or
(c) a corporation in which 2 or more persons, each of whom is an individual not ordinarily resident in Australia, a foreign corporation or a foreign government, hold an aggregate substantial interest; or
(d) the trustee of a trust in which an individual not ordinarily resident in Australia, a foreign corporation or a foreign government holds a substantial interest; or
(e) the trustee of a trust in which 2 or more persons, each of whom is an individual not ordinarily resident in Australia, a foreign corporation or a foreign government, hold an aggregate substantial interest; or
(f) a foreign government; or
(g) any other person, or any other person that meets the conditions, prescribed by the regulations. [...]
substantial interest: a person holds a substantial interest in an entity or trust if:
(a) for an entity—the person holds an interest of at least 20% in the entity; or
(b) for a trust (including a unit trust)—the person, together with any one or more associates, holds a beneficial interest in at least 20% of the income or property of the trust.
[...]
40 Meaning of significant action—entities
(1) An action is a significant action if the conditions in this section are met.
First condition—kinds of action
(2) The first condition is that the action is any of the following:
(a) to acquire a direct interest in an Australian entity that is an agribusiness;
(b) to acquire interests in securities in an entity;
(c) to issue securities in an entity; [...]
Second condition—threshold
(3) The second condition is that the threshold test is met in relation to the entity (see Subdivision B of Division 4).
Third condition—kinds of entities covered
(4) The third condition (except if paragraph (2)(a) applies) is that the entity is the following:
(a) for an acquisition of interests in shares or an issue of shares:
(i) a corporation that is a relevant entity that carries on an Australian business, whether alone or together with one or more other persons; or
(ii) the holding entity of such a corporation;
(b) for any other action relating to a corporation:
(i) an Australian corporation that carries on an Australian business, whether alone or together with one or more other persons; or
(ii) the holding entity (other than a foreign corporation) of such a corporation;
(c) for an action relating to a unit trust:
(i) an Australian unit trust; or
(ii) a holding entity of an Australian unit trust.
Last condition—action taken by a foreign person
(5) If paragraph (2)(a) applies, the last condition is that the action is or is to be taken by a foreign person.
Last condition—action results in change in control
(6) If any of paragraphs (2)(b) to (e) apply, the last condition is that there would be or has been a change in control of the entity as a result of the action (see Subdivision C of Division 4).
41 Meaning of significant action—businesses
(1) An action is a significant action if the conditions in this section are met.
First condition—kinds of action
(2) The first condition is that the action is any of the following:
(a) to acquire a direct interest in an Australian business that is an agribusiness;
(b) to acquire interests in assets of an Australian business; [...]
Second condition—threshold
(3) The second condition is that the threshold test is met in relation to the Australian business (see Subdivision B of Division 4).
Third condition—action taken by a foreign person
(4) If paragraph (2)(a) applies, the third condition is that the action is or is to be taken by a foreign person.
Third condition—action results in change in control
(5) If paragraph (2)(b) or (c) applies, the third condition is that there would be or has been a change in control of the business as a result of the action (see Subdivision C of Division 4).
[...]
47 Meaning of notifiable action—general
(1) An action is a notifiable action if the conditions in this section are met.
First condition—kinds of action
(2) The first condition is that the action is any of the following:
(a) to acquire a direct interest in an Australian entity or Australian business that is an agribusiness;
(b) to acquire a substantial interest in an Australian entity;
(c) to acquire an interest in Australian land.
(3) The second condition is that the threshold test is met in relation to the entity, business or land (see Subdivision B of Division 4).
Third condition—kinds of entities covered
(4) If paragraph (2)(a) or (b) applies, the third condition is that the entity is:
(a) an Australian corporation that carries on an Australian business, whether alone or together with one or more other persons; or
(b) an Australian unit trust; or
(c) an Australian entity that is the holding entity of an entity mentioned in paragraph (a) or (b).
Last condition—action taken by a foreign person
(5) The last condition (whether paragraph (2)(a), (b) or (c) applies) is that the action is or is to be taken by a foreign person.
[...]
51 The threshold test for entities and businesses
The threshold test is met in relation to an entity or business for a significant action mentioned in column 1 of the following table if the value mentioned in column 2 of the table is more than the value prescribed by the regulations.
[see legal source for table]
[...]
67 Order prohibiting proposed significant actions
(1) The Treasurer may, by notifiable instrument, make an order under subsection (2) if the Treasurer is satisfied that:
(a) a significant action is proposed to be taken; and
(b) taking the significant action would be contrary to the national interest.
(2) The Treasurer may make an order in accordance with the following table.
[see legal source for table]
[...]
81 Compulsory notice of notifiable actions
(1) A foreign person who proposes to take a notifiable action must give a notice to the Treasurer before taking the action.
(2) If a person takes an action by entering an agreement, the notice must deal with each notifiable action covered by the agreement." (Foreign Acquisitions and Takeovers Act 1975 (Act No. 92 of 1975), last amended by Act No. 61, 2018, Sections 4, 40, 41, 47, 51, 67 and 81)
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"22 Businesses that are sensitive businesses
(1) This section prescribes conditions for subsection 26(1) of the Act.
(2) A business is a sensitive business if:
(a) the business is carried on wholly or partly in any of the following sectors (including such a business relating to infrastructure for those sectors):
(i) media;
(ii) telecommunications;
(iii) transport; or
(b) the business is wholly or partly:
(i) the supply of training or human resources to, the manufacture of military goods, equipment or technology for, or the supply of military goods, equipment or technology to, the Australian Defence Force or other defence forces; or
(ii) the manufacture or supply of goods, equipment or technology able to be used for a military purpose; or
(iii) the development, manufacture or supply of, or the provision of services relating to, encryption and security technologies and communications systems; or
(iv) the extraction of (or the holding of rights to extract) uranium or plutonium or the operation of a nuclear facility.
[...]
28 Application of this Division
This Division applies to the provisions of the Act, other than:
(a) the definition of foreign person in section 4 of the Act; and
(b) any other provision of the Act to the extent that it relates to that definition.
The provisions of the Act that this Division applies to are the excluded provisions.
[...]
31 Australian businesses carried on by or land acquired from government
(1) The excluded provisions do not (subject to subsection (2)) apply in relation to an Australian business that is carried on (whether alone or together with one or
more other persons) by, or an acquisition of an interest in Australian land from, any of the following persons:
(a) the Commonwealth, a State, a Territory or a local governing body;
(b) an entity wholly owned by the Commonwealth, a State, a Territory or a local governing body.
(2) However, subsection (1) does not apply in relation to:
(a) an acquisition of an interest by a foreign government investor; or
(b) an acquisition of an interest in Australian land if the interest is, or includes, an interest in any of the following infrastructure:
(i) public infrastructure, except in relation to public roads;
(ii) infrastructure for existing or proposed roads, existing or proposed railways, or existing or proposed inter-modal transfer facilities, within the National Land Transport Network (within the meaning of the National Land Transport Act 2014);
(iii) infrastructure for existing or proposed roads, existing or proposed railways, or existing or proposed inter-modal transfer facilities, that are designated under a law of a State or Territory as either significant or controlled by the State or Territory;
(iv) the infrastructure (or part of the infrastructure) of a telecommunications network;
(v) a nuclear facility; or
Note: The infrastructure mentioned in this paragraph is relevant to national security.
(c) an Australian business that holds an interest in Australian land to which paragraph (b) applies.
[...]
51 Taking action in relation to entities and businesses
The following table prescribes values for section 51 of the Act (entities and businesses) to the extent that that section relates to items 2 to 5 of the table in that section. [see legal source for table]" (Foreign Acquisitions and Takeovers Regulation 2015 (SLI 2015 No. 217), last amended 19 December 2017, Sections 22, 28, 31 and 51)
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"6 Meaning of interest and control information
(1) The following information is interest and control information in relation to an entity (the first entity) and an asset (subject to subsection (3)): [...]
(e) the type and level of the interest the first entity holds in the asset;
(f) information about the influence or control the first entity is in a position to directly or indirectly exercise in relation to the asset;
[...]
9 Meaning of critical infrastructure asset
(1) An asset is a critical infrastructure asset if it is:
(a) a critical electricity asset; or
(b) a critical port; or
(c) a critical water asset; or
(d) a critical gas asset; or
(e) an asset declared under section 51 to be a critical infrastructure asset; or 
(f) an asset prescribed by the rules for the purposes of this paragraph. [...]
(3) The Minister must not prescribe an asset for the purposes of paragraph (1)(f) unless the Minister is satisfied that:
(a) the asset is critical to:
(i) the social or economic stability of Australia or its people; or
(ii) the defence of Australia; or
(iii) national security; and
(b) there is a risk, in relation to the asset, that may be prejudicial to security.
[...]
26 Meaning of notifiable event
An event is a notifiable event in relation to a critical infrastructure asset if:
(a) the event has the effect that either of the following previously obtained by the Secretary for the purposes of this Act becomes incorrect or incomplete:
(i) the operational information in relation to the asset;
(ii) the interest and control information in relation to a direct interest holder and the asset; or
[...]
32 Direction if risk of act or omission that would be prejudicial to security
(1) This section applies if in connection with the operation of, or the delivery of a service by, a critical infrastructure asset the Minister is satisfied that there is a risk of an act or omission that would be prejudicial to security.
Direction to do, or refrain from doing, an act or thing
(2) The Minister may, subject to subsections (3) and (4), give an entity that is a reporting entity for, or an operator of, a critical infrastructure asset a written direction requiring the entity to do, or refrain from doing, a specified act or thing within the period specified in the direction.
[...]
51 Declaration of assets by the Minister
(1) The Minister may, in writing, declare a particular asset to be a critical infrastructure asset if:
(a) the asset is not otherwise a critical infrastructure asset; and
(b) the asset relates to a relevant industry; and
(c) the Minister is satisfied that:
(i) the asset is critical infrastructure that affects national security; and
(ii) there would be a risk to national security if it were publicly known that the asset is critical infrastructure that affects national security." (Security of Critical Infrastructure Act 2018 (Act No. 29 of 2018), Sections, 6, 9, 26, 32, and 51)
Foreign Acquisitions and Takeovers Act 1975 (Act No. 92 of 1975), last amended by Act No. 61, 2018, Sections 4, 40, 41, 47, 51, 67 and 81
Foreign Acquisitions and Takeovers Regulation 2015 (SLI 2015 No. 217), last amended 19 December 2017, Sections 22, 28, 31 and 51
Security of Critical Infrastructure Act 2018 (Act No. 29 of 2018), Sections, 6, 9, 26, 32 and 51
[<a href="https://www.legislation.gov.au/C2004A01402/2018-09-18/text">Act</a>],[<a href="https://www.legislation.gov.au/F2015L01854/2017-12-15/text">Reg</a>],[<a href="https://www.legislation.gov.au/C2018A00029/asmade/text">Act</a>]