Three of Britain’s former Northern Ireland secretaries are warning Prime Minister Boris Johnson to sort out the wrangling over Brexit or continue to be snubbed by Joe Biden on steel tariffs.

Ex-Cabinet ministers from across the political divide urged the prime minister to take heed of his U.S. counterpart’s protective approach to Northern Ireland, which faces turmoil over its post-Brexit trade arrangements.

Biden has been refusing to negotiate with Britain over punishing Donald Trump-era steel and aluminum tariffs despite doing a deal with the EU on the issue. Reports suggest he is also preparing to talk to Japan, which wants its own agreement.

Meanwhile, the Protocol was agreed in the Brexit deal to avoid a politically-sensitive hard border between Northern Ireland, part of the U.K., and the Irish Republic, an EU member state.

But Britain has been pressing for changes, arguing the arrangement is disrupting business and exacerbating sectarian tension. The EU has said it is open to technical tweaks, but reiterated that the arrangement is needed to protect its single market.

The U.K. government insists the Protocol and the steel issues are not linked. But a U.S. memo leaked to the Financial Times last month said Washington was unwilling to discuss the steel matter until the Northern Irish protocol negotiations are concluded. It is clear the U.S. is not in a rush to resolve the issue.

There are also concerns that U.K. government moves to end prosecutions linked to “the Troubles” — the long and bloody conflict between unionists and Irish republicans — are another aggravating factor in Washington.

“No.10 [Downing Street] should not underestimate Biden’s commitment to Northern Ireland,” Peter Mandelson, a former Northern Ireland secretary during the New Labour era, told POLITICO. “If Johnson jeopardizes stability and the upholding of treaty obligations this will have systemic repercussions for the U.S.-U.K. relationship.”

Paul Murphy, who also served in the job under Tony Blair, declared: “The sooner we can resolve the issue with the Protocol, the sooner we can resolve the issue on trade.” He argued there had been “too much megaphone diplomacy” on the Protocol issue and “it needs a proper resolution and prime ministerial intervention.”

Julian Smith, who was the first Cabinet minister to serve in the Northern Ireland Office under Johnson, said on Twitter that resolving the Northern Ireland protocol issue “ASAP and in a balanced way will unlock a lot of U.S. issues.”

A fourth former Northern Ireland Secretary, Theresa Villiers, insisted the U.K. needed to explain to Washington that the Protocol, which has drawn an effective trade border between Great Britain and Northern Ireland, must be renegotiated to protect the peace deal.

“The Americans have a longstanding interest in the Belfast Agreement, but maintaining the Protocol is undermining that agreement because it has changed the status of Northern Ireland in the UK, without the consent of the people,” she said.

“The U.K. Government needs to engage closely and actively with Washington to explain why changing the Protocol is needed to maintain the integrity of the Belfast Agreement.”