The Green Party says there need to be tougher rules are needed on the sale of marine farming ventures to foreigners.
Primary production spokesperson Steffan Browning says a gap in legislation allows foreign investment in aquaculture to bypass the Overseas Investment Office process.
By law, sale of the Crafar family farms to a Chinese company required OIO approval, but an application by Malaysian-controlled King Salmon to expand its operation to include nine more marine farms in the Marlborough Sounds, does not.
He's preparing a private members bill to push for the inclusion of aquaculture in the legislation.
King Salmon wants to increase its water space by 11 hectares to 17 in the 150,000 hectare Marlborough Sounds.
Public submissions to the Environmental Protection Authority on the company's proposal to add nine farms to its existing five ended last week.
An independent board of inquiry is expected to make a decision by December.