Labour's shadow cabinet could be set to shift its position on a further Brexit referendum after a meeting on Tuesday.
The party's leader, Jeremy Corbyn, has faced calls to move policy in a more pro-EU direction.
On Monday, trade union leaders backed a referendum on any deal agreed by the Tory government or a no-deal exit from the EU.
They are now calling for Remain to be on the ballot and expect Labour to support that option.
If Labour wins power in a general election, they want a "confirmatory vote" on any new deal negotiated.
However, Labour's stance in a referendum campaign in these circumstances would "depend on the deal negotiated".
Mr Corbyn has previously said he would consult the unions before making any shift in Labour policy.
The shadow cabinet is due to meet at 10:00 BST.
Deputy leader Tom Watson and other leading figures have called for an unambiguously pro-Remain stance amid criticism that confusion over Labour's message contributed to its poor performance in the recent European parliament elections.
But MPs from Leave areas of the UK have warned it could damage the party's election performance.
On Monday, Mr Watson welcomed the agreement by the bosses of Labour's five-biggest affiliated unions as a "step in the right direction", but said his party should not be supporting any form of Brexit.
In a document seen by the BBC, Unite, Unison, the GMB, CWU and Usdaw appear to have moved towards the position advocated by Mr Watson and others by saying that "Remain" should be an option on the ballot paper, and Labour should campaign for it.
In the event of a snap election and a Labour victory, they would expect the new government to negotiate a deal to leave the EU - a position favoured by the Unite union.
However, the deal should be put to a confirmatory vote - a position favoured by Unison and the GMB - and in this scenario "Remain" should also be an option on the ballot paper.
Mr Corbyn has previously said he would be prepared to back a referendum on any Brexit deal put to Parliament.
Mr Corbyn has not guaranteed either to campaign for the UK to stay in the EU or confirmed that this would even be an option on the ballot paper.
The Conservatives said Labour had "no interest in delivering on the referendum result" of 2016.
"Labour promised to respect the Brexit vote, but rerunning the referendum and backing remain would be an attempt to frustrate Brexit and ignore the democratic mandate to deliver it," a spokesman said.
Analysis by Iain Watson
Brexit is the fourth item on the shadow cabinet agenda, but it's likely to dominate the discussion.
Jeremy Corbyn has been under huge pressure to change position on Brexit following a poor result in the European elections.
The unions' call for the party to campaign to remain if a referendum is foisted on a new Conservative leader stands a good chance of gaining shadow cabinet support - even though some MPs in Leave areas won't like it.
But the unions' position on what happens in the event of snap election could prove more problematic.
If Labour were to win, then the unions say an incoming government should negotiate its own Brexit deal.
But the party's deputy leader Tom Watson has said that not even a Labour deal would be as good as Remain.
And the proposal to put any Labour-brokered agreement to a referendum has also raised eyebrows amongst some MPs.
The prominent leave campaigner, Kate Hoey called it "utterly stupid", while some anti-Brexit Labour politicians want guarantees that they could campaign against their own party's deal without being suspended or expelled.
