Just hours before Theresa May heads to Brussels to put the final touches to a Brexit deal with Commission President Jean-Claude Juncker, negotiators are still grappling with major points of disagreement between the two sides — notably on fisheries, Gibraltar and the rules governing trade in goods.

Intense discussions continued Tuesday night, with the talks centering on May’s controversial proposal for the U.K. to stay effectively within the EU single market for goods but not services, three EU27 diplomats confirmed.

EU leaders have long referred to that as a threat to the integrity of the single market and in a briefing for ambassadors Tuesday night, Sabine Weyand, the EU deputy chief negotiator, sought to reassure member countries. She said Brussels would stick to its red lines, telling them the EU was “not compromising on anything.”

“We are not stuck. We’re still working on it. Goods will be discussed tonight [Tuesday],” said one EU diplomat.

The U.K.’s proposal is to maintain a free-flowing goods trade by adopting a common rule book with the EU, while removing trade tariffs and quotas. That is central to the so-called Chequers plan agreed by the U.K. Cabinet in July at May’s eponymous country residence.

The plan is unpopular with Brexiteers in her own party because it will mean that after Brexit the U.K. is subject to EU rules that is has no control over, but it is central to May’s aim of maintaining near frictionless trade in goods with the bloc. For the EU, it would jeopardize the single market by allowing unfair competition for British businesses.

While ambassadors were united in their desire to defend the integrity of the EU single market, there were also signs at the meeting of tensions between member countries over the final stages of the talks. While Spain has made no secret in recent days that it is not happy with the wording on future negotiations regarding Gibraltar, the diplomat from one founding EU27 country warned against pushing the U.K. too far and insisting on a text it could not sign up to. The diplomat said his country’s leader would only attend a hastily convened special summit in Brussels on Sunday if the agreement had been finalized by then.

“Leaders cannot be involved in drafting and some of them have made clear they will show up only if the deal is closed,” said a second EU diplomat.

The talks are now focused less on the 585-page draft Withdrawal Agreement published last week that sets out the legally binding terms of Britain’s departure from the EU, but more on the political declaration that will be agreed alongside it. A much vaguer seven-page summary of that document setting out an outline of the U.K.’s future relationship with the bloc has already been made public. Weyand told ambassadors she now expects that text to grow to 22 or 23 pages.

May has herself emphasized the vital nature of the document, telling the BBC on Sunday that “the thing that’s going to make a difference to people’s lives is the future relationship … It’s in the national interest to get that deal right.”

That sentiment was repeated at the meeting Tuesday evening, with one diplomat from a major EU country saying that it could not be approved by negotiators without sign off from member countries. After two years of EU27 unity during the negotiations, they could not “fall at the final hurdle,” the diplomat said.

On fisheries, Weyand told ambassadors there is still “divergence.” The U.K. wants a Norway-style arrangement where catch quotas are renegotiated on an annual basis. But it has said this will result in less access than EU27 fleets currently enjoy. France and other countries are pushing for the political declaration to make clear that a future U.K.-EU free trade deal will depend on the U.K. offering similar access to its waters as it currently does.

On Gibraltar, Weyand told ambassadors there is currently “total blockage” on the issue, one diplomat said. Spain is adamant the text must make clear that the EU’s negotiations on its future relationship with the disputed territory must be conducted separately to those with the U.K. — and that they can only proceed with Madrid’s approval.

“Spain [is] not convinced yet on Gibraltar and causing some serious waves,” one EU diplomat said. In an interview with POLITICO on Tuesday, the country’s foreign minister, Josep Borrell, said his government wants a clear statement in the text.

“There will be specific negotiations about Gibraltar between the European Union and the United Kingdom but for these agreements Spain … has to agree,” he said.

On other specific points, Weyand said the political declaration will include: a statement on cooperation between the U.K. Civil Aviation Agency and its EU counterpart the European Aviation Safety Agency to avoid travel disruption; U.K. participation in the Galileo satellite program, but only as a third country; a governance arrangement for the future relationship similar to the Withdrawal Agreement, with the European Court of Justice acting as the sole arbiter of EU law. The only exception to that would be “when national security is at play,” said one EU diplomat who spoke to POLITICO.

If Juncker and May are able to conclude a deal at their meeting Wednesday afternoon, EU ambassadors will meet again on Thursday to discuss the final text. A separate meeting of prime ministerial EU advisers (so-called sherpas) will happen Friday so that leaders can be briefed on the final deal before the Sunday summit, at which the full package will receive formal sign off. At that point it will still need to be ratified by the U.K. and EU parliaments.

A U.K. government official declined to comment on which topics were dominating the final stages of the talks, saying only: “Negotiations are ongoing.”