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'. The acquisition of a direct interest in an Australian entity or business that is an agribusiness by a foreign person constitutes a significant action if a monetary threshold is met. Such acquisitions must be notified to the Treasury before the action can be taken. Agribusiness, as defined in the Foreign Acquisitions and Takeovers Regulation 2015, covers entities and businesses in agriculture, forestry, fishing and certain food product manufacturing activities. Acquisition of a direct interest in an agribusiness generally refers to acquiring an interest of at least 10% in the entity or business. In principle, for an agribusiness acquisition to fall under investment screening, the value of the proposed investment must exceed a monetary threshold (55 million dollars, 2018). An exemption applies to investors from specified trade agreement partner countries, who are not subject to the rules regarding agribusinesses, but are instead subject to the requirements for significant and notifiable actions for general business acquisitions, to which a higher monetary threshold applies.
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. 
"4  Dictionary of definitions
In this Act: […]
agribusiness: an Australian entity or Australian business is an agribusiness in the circumstances prescribed by the regulations. […]
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.
[...]
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; [...]
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.
[...]
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; [...]
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.
[...]
44  Meaning of significant action—actions prescribed by the regulations
(1) The regulations may provide that a specified action is a significant action (including by providing that a specified action is a significant action if specified conditions are met).
[...]
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; [...]
Second condition—threshold
(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.
48  Meaning of notifiable action—actions prescribed by the regulations
(1) The regulations may provide that a specified action is a notifiable action (including by providing that a specified action is a notifiable action if specified conditions are met).
[...]
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] [...]
(3) If the Treasurer makes an order under subsection (2), the Treasurer may, by notifiable instrument, also 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 18 September 2018, Sections 4, 40, 41, 44, 47, 48, 51, 67, and 81)
-----------------------------
"12  When an Australian entity or Australian business is an agribusiness
(1) For the definition of agribusiness in section 4 of the Act, the following table prescribes the circumstances in which an Australian entity or Australian business is an agribusiness. [see legal source for table] [...]
(3) The business must be carried on wholly or partly in any of the following classes of the Australian and New Zealand Standard Industrial Classification Codes:
(a) any of the classes in Division A (agriculture, forestry and fishing);
(b) any of the classes in Subdivision 11 of Division C (food product manufacturing), other than any of the following:
(i) class 1113 (cured meat and smallgoods manufacturing);
(ii) class 1132 (ice cream manufacturing);
(iii) class 1162 (cereal, pasta and baking mix manufacturing);
(iv) a class in group 117 (bakery product manufacturing);
(v) class 1182 (confectionery manufacturing);
(vi) a class in group 119 (other food product manufacturing).
[...]
16  Meaning of direct interest in an entity or business
For the definition of direct interest in section 4 of the Act, a direct interest in an entity or business is:
(a) an interest of at least 10% in the entity or business; or
(b) an interest of at least 5% in the entity or business if the person who acquires the interest has entered a legal arrangement relating to the businesses of the person and the entity or business; or
(c) an interest of any percentage in the entity or business if the person who acquired the interest is in a position:
(i) to influence or participate in the central management and control of the entity or business; or
(ii) to influence, participate in or determine the policy of the entity or business.
[...]
40  Action relating to agribusinesses and agricultural land for certain investors
Relevant agreement country investors—exemption in relation to agribusinesses
(1) Paragraphs 40(2)(a) and 41(2)(a) (significant action in relation to agribusinesses) of the Act, and any other provision of the Act to the extent that it relates to those paragraphs, do not apply in relation to relevant agreement country investors
[...]
50  Certain actions taken in relation to agribusinesses
The following table prescribes a value for section 51 of the Act (agribusinesses) to the extent that that section relates to item 1 of the table in that section.
Threshold value for certain actions taken in relation to agribusinesses
Item | For action taken by ... | the value (in millions of dollars) is ...
1 | any foreign person | 55 [...]" (Foreign Acquisitions and Takeovers Regulation 2015 (SLI 2015 No. 217), last amended 30 December 2018, Sections 12, 16, 40, and 50)
Foreign Acquisitions and Takeovers Act 1975 (Act No. 92 of 1975), last amended 18 September 2018, Sections 4, 40, 41, 44, 47, 48, 51, 67, and 81
Foreign Acquisitions and Takeovers Regulation 2015 (SLI 2015 No. 217), last amended 30 December 2018, Sections 12, 16, 40, and 50
[<a href="https://www.legislation.gov.au/C2004A01402/2018-09-18/text">Act</a>],[<a href="https://www.legislation.gov.au/F2015L01854/2018-12-30/text">Reg</a>]