As tens of thousands of Australians embark on the Good Friday ritual of buying a fish meal, Senator Boswell warned they could unwittingly be served up catfish from Vietnam.
He said this could be "easily fixed by one little word saying imported or local".
It would also apply to cafes and restaurant menus.
But, while Senator Boswell declared the plan to batter imports would be a "priority" for an Abbott government, it was not the Coalition's formal policy and small business spokesman Bruce Billson said it would involve too much red tape. He said customers should just ask the fish-and-chip shop owner.
Supermarkets and other shops are already required to have country-of-origin labels on uncooked seafood but only the Northern Territory requires a sign on cooked fish.
Federal Fisheries Minister Joe Ludwig accused the Coalition of having a plan to make consumers pay more for seafood.
Senator Boswell said seafood lovers "are prepared to pay extra for Australian seafood" and a sign would help the struggling fishing industry, which was battling to compete with cheap imports.
"When someone goes into a fish-and-chip shop and buys a piece of fish it could have come from anywhere," he said.
Mr Billson said Senator Boswell's plan would mean extra red tape and compliance costs on small business.
Senator Ludwig said shops could voluntarily put signs on cooked seafood but opposed a mandatory plan.
