Opposition Leader Bill Shorten has rejected his deputy's call to force Labor MPs and senators to support same-sex marriage.

Tanya Plibersek wants the ALP members of Parliament made to follow the party's policy and vote for gay marriage.

Labor currently allows a conscience vote on the issue in Parliament.

Some Labor MPs are considering if they would cross the floor over the issue and risk expulsion from the party.

Mr Shorten said while he supports same-sex marriage, colleagues who do not should not be made to vote for it.

"I think we have waited too long in this country for marriage equality," Mr Shorten said.

"I do believe that the best way to achieve it, though, is not to force people to agree with it but to convince people."

Mr Shorten also talked down any friction with Ms Plibersek, who spoke publicly on the issue earlier this week while Mr Shorten was out of the country and she was acting leader.

She is set to push the issue at Labor's national conference in Melbourne in July.

"Tanya and I are both very committed to marriage equality," Mr Shorten said.

"I certainly have a view, though, that the best way to win the argument on marriage equality is to convince people not force them, but Tanya's got a very long track record of speaking on this issue.

"I don't think anything she said is any different to what she's said before."

Members of Labor's left faction have this week publicly backed scrapping the conscience vote.

Victorian senator Kim Carr is a senior member of the left faction and a same-sex marriage supporter, but said he did not expect the party's position to change.

"These matters will be discussed at the national conference," Senator Carr said.

"Bill's position, I think, has been articulated and carried by the last national conference and I would be surprised if the position that he's taken at this conference will be any different."