Call on PM to save same-sex marriage bill

Labor MP Terri Butler has called on the prime minister to allow a free vote on cross-party bill for same-sex marriage

A Labor MP has wants Malcolm Turnbull to allow a free vote on a cross-party bill on gay marriage. (AAP)

The Labor MP co-sponsoring a cross-party bill to legalise same-sex marriage wants Malcolm Turnbull to use his new influence over the Liberal party.

"I say to the prime minister, if you have any authority at all in your party room, then show some leadership ... get your party to agree to a free vote," Terri Butler told reporters in Canberra on Monday.

The bill has been on life support since the previous Abbott government opted for a plebiscite after the next election to decide the issue.