Several members of the US fiscal commission are asking for a commitment from Harry Reid, the Democratic Senate majority leader, and John Boehner, the future Republican speaker of the House, to hold a vote on a final package to shrink the US budget deficit in the new Congress.

According to people familiar with the matter, both Republicans and Democrats on the panel have suggested that Erskine Bowles and Alan Simpson, co-chairs of the commission, receive additional assurances from congressional leaders that they would be prepared to vote next year on a proposal that garners a majority of 14 votes out of 18 on the commission.

At the moment, Mr Reid and Nancy Pelosi, the Democratic speaker of the House, have pledged to hold a vote on a commission package in the “lame-duck” session of Congress, which began on Monday and ends next month.

A promise from Mr Reid and Mr Boehner to hold a vote on a package next year could strengthen the political momentum in favour of a deal on the commission in time for the December 1 deadline, following attacks from both the left and the right on initial recommendations by Mr Bowles and Mr Simpson.

In addition, there are concerns that even if the commission reaches a majority consensus of 14, some technical factors – such as demands from lawmakers for Congressional Budget Office scoring of certain provisions – could prevent a vote from being held before the new Congress takes office in January.

“What differentiates this commission from others is the promise from the president and the congressional leadership that a 14-member agreement would lead to a vote,” Andy Stern, a commission member and former president of the Service Employees International Union now at Georgetown University, told the FT on Tuesday.

“Without that promise, people may re-evaluate and this may threaten some of the progress that has been made,” Mr Stern said.

“The best shot if it can’t be done in this Congress is for the new Congress to empower us,” Mr Stern added, speaking ahead of the first of two closed sessions of the commission set for Tuesday and Wednesday.

A spokesman for the commission said he would not “comment on internal deliberations and discussions”. Mr Reid’s office said the commitment to hold a vote in the lame-duck session still stood, adding: “As to the new Congress, we will need to talk to the Republicans and the White House.” Mr Boehner’s office did not immediately reply to a request for comment.

The main concern in the minds of some commission members is that political wrangling could cause the talks on the panel to break down entirely.

There are also worries, however, that some panel members may attempt to seek separate votes on different recommendations to shrink the deficit instead of a single package.

These options would then most likely be taken up in the next Congress through the budget process, which will be led by Kent Conrad, the Democratic chairman of the Senate budget committee, and Paul Ryan, the Republican set to lead the House budget committee.

That could mean further political wrangling and possibly changes to commission proposals.