A leaked copy of the final draft of Britain’s new terms with the EU showed a rift between member states and European Council President Donald Tusk, the Guardian reported Thursday, as U.K. Prime Minister David Cameron readies to hold “now or never” talks with EU officials in Brussels later in the day.

A series of leaked documents showed that differences between Britain and the rest of the bloc were widening, with east-European countries like Poland protesting U.K.'s proposal to stop payments of benefits to migrants. Meanwhile, France expressed concern that Britain requested special protection so that London remained Europe’s financial center in case the country decided to part ways with the union, according to the Guardian.

Late Wednesday, Tusk told BBC in an interview EU leaders had "no choice" but to agree to a deal on Cameron's proposed reforms. However, in a letter to EU leaders Wednesday, Tusk wrote: “there is still no guarantee that we will reach an agreement. We differ on some political issues and I am fully aware that it will be difficult to overcome them.”

Meanwhile, Cameron’s bid to secure reforms in Britain's relations with the EU had reached "crunch time", a UK government official told BBC.

As negotiations to prevent Brexit enter their final stretch, an agreement on measures to restrict migration to the UK remained the toughest to reach.

European Commission President Jean-Claude Juncker proposed earlier that EU countries should be allowed to apply for an “emergency brake” to ban the payment of in-work benefits to migrants, but only after getting permission from the EU. Juncker’s second proposal was to change the EU’s definition of “a worker” so that low-paid migrants earning less than about 7,000 pounds (about $10,000) a year would not be eligible for in-work benefits.

Cameron, who has struggled to raise support for the reforms from an increasingly skeptical British public, spent the last few weeks touring European capitals to secure a deal that could be hailed as a victory back home. If he wins the concessions from the EU, he would start a domestic campaign to keep Britain inside the bloc. However, EU officials reportedly expressed concerns that Britain was setting a precedent which could lead other countries to demand changes to their membership agreements.