Supporters of a second referendum are calling on Labour’s ruling body to consult grassroots members about the party’s Brexit policy.

On Tuesday, the national executive committee (NEC) holds its first full meeting this year. Activists will gather outside to hand leaflets to members, calling on them to ask the party’s half a million members what Jeremy Corbyn should do next.

Six members of the party’s international policy commission, which met recently, have written to the Labour leader and to Labour’s general secretary, Jennie Formby, calling for an online poll to guide policy.

“There are only two possible ways forward for the country from here: a different Brexit deal or stopping Brexit,” says the letter, seen by the Guardian.

If Labour’s amendment fails to secure the backing of MPs on Tuesday “there will be no other way to avoid catastrophe (of a no-deal or a May-deal Brexit) than holding a public vote,” it says.

The signatories, who did not wish to be named before the NEC’s discussions, said: “It is our view that there should be an online poll of party members in order to confirm whether there is an appetite for a public vote: specifically a referendum containing the option to remain in the EU. As the consultation on the bombing of Syria demonstrated, it could be held in a short period of time.”

Polling suggests Labour members overwhelmingly support a “people’s vote”, with the hope of overturning the result of the 2016 referendum.

The party’s leadership has edged towards the idea, including by tabling an amendment to Theresa May’s Brexit motion calling for MPs to be given a vote on options, including a call for a public vote. But Corbyn is still prioritising securing Labour’s alternative Brexit deal and continuing to press for a general election.

People’s vote supporters in parliament opted last week to cancel plans for tabling their own amendment to May’s motion, fearing they could not secure a majority without Corbyn’s support.

Mike Buckley, the director of campaign group Labour for a People’s Vote, said: “Labour is a proudly democratic party, with policy set by our members. Our conference policy states that we should now consider options – and to take the one most likely to stop the Tories’ Brexit plans.

“Now is the time to consult members – either by a special conference, so that unions also get a say, or through an online poll. Sixty days from disaster, there is no excuse for delay.”

Corbyn has been an enthusiastic supporter of increasing the involvement of party members as a longtime member of the Campaign for Labour Party Democracy. But he and some of his close allies are acutely conscious of what they regard as the party’s obligations to represent leave voters in Labour heartland constituencies, as well as ardent remainers among the membership.

More than a dozen MPs, including frontbenchers, met Labour’s chief whip last week to warn that they would not be prepared to back a second referendum. Some, including the Great Grimsby MP, Melanie Onn, said they would resign rather than support such a move.