European Commission President Jean-Claude Juncker said on Friday that “every effort” must be made to find a way through the Brexit condundrum ahead of a crucial vote next week by British lawmakers.

Prime Minister Theresa May is facing defeat when MPs vote Tuesday on her draft divorce deal, which has aroused fierce opposition from EU supporters and Brexit enthusiasts alike.

Brussels and London are in “constant” contact to see what assurances the EU can give to persuade British MPs to back the deal, Juncker said, but he reiterated the oft-repeated warning that the deal struck in November is not up for renegotiation.

“We are in constant contact - the commission and myself - with 10 Downing Street and we will see on Tuesday what conclusions the British parliament reaches on the texts that have been proposed,” Juncker said at a press conference in Bucharest to mark the start of Romania’s stint at the helm of the rotating EU presidency.

“No deal would be a catastrophe both for our British friends and for continental Europeans, so every effort must be made between now and Tuesday to bring this important issue to a good conclusion.” May, under increasing pressure to rule out a “no-deal” Brexit, in which Britain crashes out without an agreement with the EU to ensure a smooth, orderly departure, on Thursday repeated her warning that the only way to ensure this was to back her deal.

Brexit-supporting Conservative MPs are opposed to the deal, arguing it leaves the country too closely tied to Europe, and May has already pulled the vote once with defeat looming. Asked about reports of a letter to London offering assurances about the controversial Irish “backstop” arrangement, which has inflamed Brexiteer MPs, Juncker said he would not get into “speculation and guessing games”.

“We have said - both the European Council and the commission in full harmony -- that there can be no renegotiation, but there can be clarifications,” Juncker said.