BRUSSELS ― The European Parliament’s four centrist groups have demanded European Commission President Ursula von der Leyen make major changes to her plan for the EU’s next seven-year budget, according to a letter sent on Thursday morning, obtained by POLITICO.

The groups are threatening to reject a key part of the 2028-2034 budget in the next plenary on Nov. 12 unless their conditions are met in a new amended proposal from the Commission.

Lawmakers oppose the Commission’s “national plans,” an idea to pool funds for farmers and regions — which make up around half of the total EU budget, worth €1.8 trillion — into single pots managed by the bloc’s 27 governments. This is a change from the current system, where regions play a crucial role in handling the funding.

A formal rejection would be a major blow to the Commission, as it would force the executive to propose an amended version. Political groups hope the Commission amends the proposal itself before having to use the nuclear option.

In the letter — signed by the conservative European People’s Party chief Manfred Weber, the Socialists’ Iratxe García, the centrist Renew Europe’s Valérie Hayer, and the Greens’ Bas Eickhout — the political group leaders argue that the Parliament has warned the Commission since the start of negotiations that they were against the national plans idea.

“This is unfortunately and clearly what the Commission has proposed. The European Parliament cannot accept this as a basis for starting negotiations,” the letter, the drafting of which was reported by POLITICO on Tuesday, reads.

The letter is a last-ditch attempt at increasing pressure on the Commission after weeks of stalled negotiations.