(Bloomberg) -- The European Union isn’t budging on the U.K.’s Brexit deal, as officials fear Prime Minister Theresa May will make repeated calls for concessions into the new year.

EU leaders plan only a minimal response at a summit this week to help May sell the agreement to Parliament, and European diplomats acknowledge privately that it’s unlikely to be enough to win over U.K. lawmakers.

That raises the prospect of May coming back for more as the Jan. 21 deadline for a final vote nears.

Michel Barnier, the EU’s chief Brexit negotiator, told European commissioners on Tuesday that the chances of the U.K. crashing out without a deal has increased since May postponed a parliamentary vote on the deal, a person familiar with the meeting said.

Struggling to sell the agreement to a hostile parliament, May embarked on a whistle-stop tour of northern Europe on Tuesday, holding talks with Dutch Prime Minister Mark Rutte, German Chancellor Angela Merkel and EU presidents Donald Tusk and Jean-Claude Juncker. She got similar messages from them all.

While the EU is open to providing fresh assurances over the backstop agreement that aims to prevent a hard Irish border, they won’t reopen negotiations on the substance of the deal. And they won’t make the backstop temporary, as May is asking.

“We don’t want the backstop to be used and if it is we want to be certain that it is only temporary,” she said in an interview with Sky News in Brussels. “It is those assurances that I will be seeking from fellow leaders over the coming days.”

In a further rebuke to May, Merkel told the prime minister she should hold talks with the EU as a whole, and not try to extract concessions from individual leaders, according to an official from the German chancellor’s Christian Democratic Union party, speaking on condition of anonymity.

Tusk said his discussion with May was “long and frank.” While the EU wants to help, “the question is how,” he said in a Twitter post. The bloc is losing patience, officials said.

May’s position at home is increasingly perilous since she enraged members of Parliament by pulling a vote on the deal that was scheduled for Tuesday. A growing number of Tories are trying to oust her, according to U.K. media reports, though it’s not clear if they have the numbers to do so.

Following the two-day summit in Brussels on Thursday and Friday, the European Commission will discuss no-deal contingency measures next week, according to a planning document published on Tuesday.

“The European Union has made a lot of concessions to make this withdrawal agreement possible,” French Europe minister Nathalie Loiseau told reporters in Brussels. “Our responsibility as leaders is also to prepare for a no deal because it is a hypothesis that is not unlikely.”

©2018 Bloomberg L.P.