LONDON — Britain and the United States have found common cause on the need to defend Ukraine from Russia, one-upping each other with shipments of weapons and waves of sanctions. The close collaboration has given new purpose to a “special relationship” that, by many accounts, had drifted since Brexit.
Now, though, Northern Ireland threatens to complicate matters.
The Biden administration is warning Britain not to precipitate a clash with the European Union over trade in Northern Ireland, saying it could weaken the West’s solidarity in helping Ukraine turn back the Russian onslaught.
A senior State Department diplomat, Derek Chollet, delivered the message in meetings at Downing Street on Friday, days after the British government served notice that it might unilaterally scrap some of the provisions in an agreement with Brussels that regulates trade with Northern Ireland.
“The last thing we want right now is a big U.K.-E.U. spat,” Mr. Chollet, the State Department’s counselor, said in an interview. “This is a moment where we should be sending a message of unity overall.”
Mr. Chollet urged London and Brussels to try to resolve their disputes over Northern Ireland “behind closed doors.” The United States, he said, believed there was scope for compromise on the trade arrangements. “Let’s try to lower the temperature,” he said. “Let’s try to move it into a negotiation.”
His warning came as the European Union threatened to respond with “all measures at its disposal” if Britain passed legislation discarding the agreement that regulates post-Brexit trade, known as the Northern Ireland protocol. That raised the specter of a trade war erupting across the English Channel at the very moment that the West is uniting to help Ukraine wage a land war farther east.
The White House as well as Ireland’s defenders on Capitol Hill have long urged Britain not to take steps on trade that could undermine the Good Friday Agreement, the 1998 treaty that ended decades of sectarian violence in the North.
Mr. Chollet, who is close to Secretary of State Antony J. Blinken, repeated that message on Friday. But he couched his warning in the context of the West’s alliance against Russian aggression, a message that might resonate with Prime Minister Boris Johnson of Britain, who has staked out a position among European leaders as a stalwart defender of Ukraine and as a friend of the country’s president, Volodymyr Zelensky.
“We have worked and will continue to work closely with the E.U. to ensure a united response to Russia’s illegal invasion of Ukraine,” a spokesman for Downing Street said. “We want to harness that spirit of cooperation to help resolve the issues with the Northern Ireland protocol.”
The government said that its overriding priority was to protect the Good Friday Agreement and that the new legislation on Northern Ireland was intended to “safeguard the hard won gains of the peace process”
Still, Britain’s threat to rip up parts of its trade agreement also drew criticism from congressional leaders, including the House speaker, Nancy Pelosi. In a statement on Thursday, she said that it was “deeply concerning that the United Kingdom is now seeking to unilaterally discard the Northern Ireland protocol.”
Ms. Pelosi repeated a longstanding threat that Congress would not approve a bilateral trade deal between the United States and Britain if the Johnson government did anything to jeopardize the Good Friday Agreement. Mr. Johnson once presented such a deal as a prime dividend of leaving the European Union.
But it is no longer clear how much leverage that gives congressional leaders. The White House has signaled that striking a deal with Britain is not high on its list of priorities, anyway. In March, the United States trade representative, Katherine Tai, described free-trade agreements as a “very 20th-century tool.”
With Britain’s trade negotiator, Anne-Marie Trevelyan, looking on, Ms. Tai said she wanted to avoid spending “a lot of blood, sweat and tears working on something that isn’t relevant to the needs of our people and our economies.”
Lawmakers insist that the United States could still use the prospect of a trade deal as a lever with Britain on Northern Ireland, given that the administration is exploring a similar deal with the European Union. They also note that President Biden, a proud Irish American who frequently invokes his roots, has personally warned Mr. Johnson about the sanctity of the Good Friday Agreement.
Russia-Ukraine War: Key Developments
Russia’s punishment of Finland. Russia will cut natural gas supplies to Finland on May 21, according to Finland’s state energy provider. Russia said that it was suspending the supply because Finland had failed to comply with its demand to make payments in rubles. Finland has also submitted an application to join NATO, angering Russia.
A delegation of Democratic and Republican lawmakers, led by Representative Richard E. Neal, Democrat of Massachusetts and the chairman of the House Ways and Means Committee, traveled to London from Brussels on Friday as part of a multiday tour to press both sides to avoid a rupture over Northern Ireland. He expressed suspicion about Britain’s motives.
“We’ve heard these repeated arguments that the U.K. wants to negotiate,” Mr. Neal, who is one of Ireland’s most vocal defenders in Congress, said in an interview. “What we heard from the E.U. today is, ‘Let’s get on with it.’”
“How the U.K. wants to handle its domestic politics, that’s up to them,” he added. “But an international agreement is an international agreement.”
British officials play down the prospect of a rift with the United States over Northern Ireland. They say the subject comes up far less in conversations with the White House than on Capitol Hill. But they also profess frustration with what some say is a failure in Washington to understand the complexities on the ground in the North, and why Britain has no choice but to overhaul the trade rules.
Mr. Johnson recently sent his minister for Northern Ireland, Conor Burns, to Washington to meet with lawmakers and other government officials. Mr. Burns told reporters he believed Britain’s message was getting through.
Privately, some British officials point out that the Republicans may take control of the House after the midterm elections this fall, which would push challenging figures like Mr. Neal out of their powerful committee chairmanships.
Asked about that, Mr. Neal said: “One, we plan to win this election. And two, Joe Biden is president until 2024.”