Labour will continue to push for a free vote, despite the government being adamant that a plebiscite is the only way to see reform on the matter.
Labour’s stance comes after the Green’s also vowed to block the legislation in August and will see the two parties team up with the Nick Xenophon Team and Derryn Hinch to block the legislation in the Senate.
"The political reality is the plebiscite is now dead," Australian Marriage Equality co-chair Alex Greenwich told SMH.
Labor will continue to push for a free vote, but the government controls the numbers in the lower house.
Malcolm Turnbull, who is in favour of same-sex marriage, risks splitting his party if he switches to a free-vote in the parliament with members threatening to withdraw their support.
"My support for the government is conditional that we honour our election commitments," said Nationals MP Andrew Broad.