Northern Ireland’s Democratic Unionist Party blocked the restoration of a power-sharing administration in the British-run province on Friday when newly elected members for the Assembly met in the Stormont chamber for the first time.

DUP leader Jeffrey Donaldson told reporters his party had decided not to support the election of a speaker until the British government and the European Union resolve issues around the Northern Ireland Protocol that governs post-Brexit trade in the region.

British government ministers have repeatedly said that the European Union must make concessions on the protocol to win over the unionist community. Irish officials have countered that a clear majority in the Northern Irish Assembly broadly support the protocol.

Under the terms of the 1998 Good Friday peace agreement that largely ended three decades of sectarian bloodshed in the region, nationalists and unionists are required to agree on a speaker before electing a cross-community government.

The DUP’s decision means the Assembly could not discuss the appointment of a First and a Deputy First Minister. The party had already said it would block the formation of an executive.

In a symbolic breakthrough for Irish nationalism, Sinn Fein replaced the DUP last week as the region’s largest party after elections for the legislature.

In a statement posted on the DUP’s website, Donaldson said unionist concerns on the Northern Ireland Protocol were not merely a political squabble, calling the protocol “a direct challenge to the principles that have underpinned every agreement reached in Northern Ireland over the last 25 years.”

When Britain quit the EU, Prime Minister Boris Johnson’s government agreed to a pact that effectively left Northern Ireland within the EU’s single market and customs union given its open border with EU member Ireland.

That created a customs border in the sea between the rest of the United Kingdom and the province, which pro-British communities in Northern Ireland say erodes their place within the UK. Britain now says the required bureaucracy is intolerable.

Michelle O’Neill, leader of Sinn Fein in Northern Ireland, said the DUP, which supported Britain’s exit from the EU, was punishing the public with its actions.

“They are disgracefully holding the public to ransom for their Brexit mess,” she said on Twitter.

“Today is the day we should be forming an Executive to put money in peoples pockets and to start to fix our health service.”