Independent senator Nick Xenophon is threatening to field lower house candidates in key Liberal-held seats in Adelaide in a move that could help Labor oust ministers Christopher Pyne and Jamie Briggs from their seats.

Senator Xenophon told Fairfax Media he would preference against the Liberals at the next federal election if the Coalition did not honour its promise to build the next generation of submarines in Australia. This could top up any Labor candidate's vote and potentially propel the opposition to victory in the key marginal seats.

Independent senator Nick Xenophon: "The whole idea is for the Libs to do the right thing on submarines." Credit:Quinn Rooney

He confirmed he would field candidates in Mr Pyne's seat of Sturt, Mr Briggs's seat of Mayo and others including Hindmarsh, which the Coalition won from Labor at the last election.

"The whole idea is for the Libs to do the right thing on submarines," he said.