HILLSBOROUGH, Northern Ireland -Sinn Fein President Mary Lou McDonald said her party had a "fairly tough" meeting with British Prime Minister Boris Johnson on Monday in which they told him taking unilateral action over post-Brexit trade rules for Northern Ireland would be wrong.

Johnson says the European Union must make concessions on the rules - known as the Northern Ireland protocol - to win over the province's unionist community loyal to the United Kingdom, and has threatened unilateral action that the EU says could start a trade war.

McDonald, whose party seeks a united Ireland and is now the region's largest after an election this month, said Johnson did not give details of any proposed legislation which would effectively ditch parts of the protocol.

"We've had what we would describe as a fairly tough meeting with the prime minister," McDonald told reporters following the talks with Johnson in Northern Ireland.

"We have said directly to him that the proposed unilateral act of legislating at Westminster is wrong. It seems to us absolutely extraordinary that the British government would propose to legislate to break the law."

Johnson agreed to the protocol in 2019 to allow Britain to leave the EU's single market and customs union without controls being re-imposed on the border between the Irish Republic and Northern Ireland, a vital part of the 1998 Good Friday peace deal that ended three decades of violence.

But the plan effectively introduced a customs borders border between Britain and Northern Ireland, incensing many unionists.

The dispute has stymied another part of that peace deal - power-sharing between Sinn Fein and the Democratic Unionist Party it beat in the election. The DUP has blocked power-sharing because of its opposition to the protocol.

Johnson, in an article published by the Belfast Telegraph newspaper on Monday, said reform of the protocol was essential for Northern Ireland to move forward.

"There is without question a sensible landing spot in which everyone's interests are protected," he said. "Our shared objective must be to the create the broadest possible cross-community support for a reformed protocol in 2024."

The EU has said that renegotiating the protocol is not an option but that it is open to joint work to bring long-term certainty.

"I hope the EU's position changes," Johnson said in his newspaper article. "If it does not, there will be a necessity to act."

"The government has a responsibility to provide assurance that the consumers, citizens and businesses of Northern Ireland are protected in the long-term. We will set out a more detailed assessment and next steps to parliament in the coming days".

Speaking to reporters, DUP leader Jeffrey Donaldson said he hoped the government would do the right thing and help restore a consensus in Northern Ireland. "It's actions that I will judge these things on not just words," he said.

  - Reuters