LONDON — The European Commission rejected UK Prime Minister Theresa May’s emerging plan for a post-Brexit trade deal, just as she tries to persuade her divided Cabinet to back it.

May is meeting with her most senior ministers to try to force them to agree the outline of a trading policy that would see the United Kingdom remain close to EU rules in many areas — such as carmaking and data sharing — while breaking away partially or fully in others, an approach known as the “three baskets.’’

It won’t work, the Commission said in a presentation published on its website.

“UK views on regulatory issues in the future relationship including ‘three basket approach’ are not compatible with the principles in the European Council guidelines,’’ one of the slides reads. If the UK “aspires to cherry pick,’’ there’s a “risk for the integrity’’ of the single market, it says.

The EU Commission’s assessment outlines the difficulties of reaching trade terms with the United Kingdom in areas including chemicals, agriculture and carmaking. Despite UK proposals for a system of “mutual recognition’’ of British and European regulations, the document suggests this would represent exactly the kind of “cherry picking’’ approach it has always ruled out.

The intervention comes at a critical time in the Brexit process, with May’s authority under pressure and time for negotiations running short.

The Conservative party is even more divided than May’s Cabinet, and without a parliamentary majority she can’t lay down the law. The risk of a leadership challenge hangs over everything she does, while she needs to spell out her blueprint for the future relationship with the EU now because talks on trade are due to start next month -- and end by October.

On Thursday, May took her most senior cabinet ministers away to her Chequers country residence to thrash out an approach to the future trade relationship that they can all agree on. Officials warn in private that the most divisive decisions may get kicked down the road.

After as many as eight hours of talks with her ministers, which officials expect to last late into the night, May hopes she’ll have won enough support from her top team to be able to go away and write a speech she’s expected to deliver next week announcing the United Kingdom’s negotiating goals.

Privately, some in May’s team are cautious that a deal will be reached. According to one official, ministers could agree to blur the details on the United Kingdom’s future relationship with the EU to preserve unity ahead of May’s speech.

But that won’t deal with the two biggest fears among the Brexit supporters in Cabinet, such as Foreign Secretary Boris Johnson. These are that the riddle of avoiding a hard border with Ireland will be used as a Trojan horse to keep Britain in a customs union with the EU, and that May will allow the European Court of Justice to keep a role overseeing regulation affecting the United Kingdom ­after Brexit.

Brexit-backers and pro-Europeans in the Cabinet have been holding meetings in pairs and small groups in an effort to reach a consensus.

Euroskeptic Tories worry May is preparing to tie the country too closely to the EU’s single market and trade rules, an outcome they’d see as a betrayal of the UK’s 2016 vote to leave the bloc. On the other side, pro-Europeans are fighting May’s plans to take Britain out of the EU’s single market and customs union.