Labor has used a US-style legislative tactic in a bid to force the federal government to build the next-generation submarine fleet in Australia.

Opposition defence spokesman Stephen Conroy on Wednesday won Senate support to tack on an amendment to an unrelated bill that prohibits the government from entering into a contract for the $50 billion project unless the successful bidder promises to build the fleet in Australia.

The amended bill goes back to the House of Representatives where the government has the numbers to vote down what it labels an "ad-hoc stunt".