Abbott forcing conscience on Aust: Shorten

Tony Abbott is forcing his conscience on the Liberal Party and the Australian people, says Opposition Leader Bill Shorten.

Thousands attended a marriage equality rally in Melbourne where they heard Mr Shorten reiterate his promise to make gay marriage legal if Labor wins the election due next year.

"Within 100 days, I will introduce a law to have marriage equality and we will get it through this time," Mr Shorten said on Saturday.

Mr Shorten said the prime minister had given into extreme right-wing voices in his party and denied his MPs the chance to vote with their conscience.

"He said he believes in a conscience vote," Mr Shorten said.

"What he didn't tell Australians is he believes in his own conscience and he will force everyone to agree with his conscience."

Greens MP Adam Bandt said Mr Abbott should get out of the way and Australia could have marriage equality by the end of the year.

"I think Tony Abbott has decided to side with a minority in the Australian community who has a loud voice but doesn't speak for the loving majority," he said.