Opposition Leader Bill Shorten is preparing to firm up Labor's plans to double Australia's refugee intake, in a move that is expected to quell some of the internal discontent over his decision to endorse the Government's policy to turn back asylum seeker boats.

Despite previously criticising the Coalition's turn-back policy, Mr Shorten has confirmed he is in favour of it.

The announcement came just days before the ALP's national conference.

"I think it's important to be honest with my party and the nation and, if I was to form a government, I would want the option of boat turn-backs — where safe to do so — on the table," Mr Shorten told Channel 7 this morning.

He will take the policy approach to this weekend's conference and ask for support from almost 400 voting delegates — a mix of MPs, grassroots members and union representatives.

The about-face has enraged some members of Labor's Left faction who feel ambushed by the decision.

MP Andrew Giles suggested the move would breach international law.

Victorian MP Anna Burke said a lot of voters would be reconsidering their support for Labor and she would not vote in favour of the change.

"I'm not in a position to support that policy," she said.

"I don't think there's a need to be trumpeting turn-backs."

Some MPs want the party to endorse a hard target for the refugee intake rather than an aspirational goal.

Labor took a humanitarian intake of 20,000 people per year to the last election.

There is a draft platform up for consideration this weekend, for the party to "aspire" to progressively increase the intake to 27,000 places a year.

That would be close to double the existing 13,750-place intake under the Coalition government.

The ABC has been told Mr Shorten will harden that language and put forward a proposal for the increase this weekend.

Labor MP Alannah MacTiernan describes herself as "non-aligned" to any particular faction.

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She is backing Mr Shorten's position in favour of boat turn-backs but says her support is conditional.

"The quid pro quo will be doubling the refugee intake," she said.

"That means the most vulnerable people around the world will have an opportunity to come to Australia."

Mr Shorten strongly hinted at an increase in the refugee intake when he announced the policy change last night.

"We will have more to say in coming days about being willing to support more refugees and to take up our burden internationally," he told the ABC's 7.30 program last night.

Labor frontbencher Stephen Conroy has acknowledged Mr Shorten will face a close contest when he asks for support for the turn-back policy.

"It is very close and there's people of goodwill on both sides who are very passionate about this," Senator Conroy told Sky News.

"I believe in the end Bill's position will carry the conference floor."

Mr Shorten is not expected to put forward a new platform to explicitly endorse turn-backs, but rather to argue the current policies do not rule the practice out.

The matter is only likely to go to a vote if those opposed to the policy put forward a specific ban on turn-backs, which the group Labor for Refugees has flagged doing.

Labor's Left faction reaffirmed its opposition to turning back asylum seeker boats after a lengthy meeting in Melbourne this afternoon.