And getting the support of U.K. lawmakers appears a particularly onerous task for Prime Minister Boris Johnson, who is set to put his deal to a rare weekend vote in the House of Commons on Saturday.

The Democratic Unionist Party — a Northern Irish group who have acted as allies to Johnson’s Conservatives — told NBC News on Thursday that they would not be supporting the plan in its current form.

“As things stand, we could not support what is being suggested,” a DUP statement said before the deal, citing disagreements over trade, taxes, and their ability to opt-out of certain parts of the arrangement. After the announcement, a spokesperson said that “our statement still stands from this morning.”

Losing the DUP’s support will make getting the deal through Parliament even harder.