The opposition party in Australia says gay Australians "will never be allowed to marry" under the current government.
Labour says an offer from the Prime Minister Tony Abbot of a referendum for the the next parliament was nothing but a "delaying tactic".
The attack comes as Mr Abbott faces criticism within his own ranks about how he has handled the issue.
Mr Abbott says the country will get a chance to vote on legalising gay marriage - if they re-elect his government next year.
His coalition has already refused to allow its lawmakers a free vote on the issue.
A debate on same-sex marriage by MPs yesterday saw strong support for those arguing to keep the status quo.
"It was roughly 60:30, 60 supporting the existing position, 30 saying there should be a free vote," he said.
Australian Marriage Equality national director Rodney Croome said: "If there is going to be a plebiscite on marriage equality, it must be at the next federal election to give the next government a clear mandate to enact marriage equality".
"Tony Abbott can gag his party room, but he can't gag the Australian people who will vote strongly in favour of marriage equality at a plebiscite".
"Any further delay is totally unacceptable, and any public vote must be at the next election so this issue is resolved as as quickly and cheaply as possible," he added.
But Mr Abbott says his party remains resolute in its position.