The leader of the small Northern Irish party that supports Prime Minister Boris Johnson’s government accused the European Union and Ireland on Tuesday of trying to trap the British territory in a permanent customs union.

“The Prime Minister’s proposals have flushed out Dublin’s real intention to trap Northern Ireland in the EU Customs Union forever,” Arlene Foster said in a statement after reports of a call between German Chancellor Angela Merkel and Prime Minister Johnson.

“We will not accept any such ultimatum or outcome.”

Merkel is reported to have told the British prime minister that a Brexit deal was “overwhelmingly unlikely” in a call on Tuesday unless Britain left Northern Ireland in the customs union.