DUBLIN (Reuters) - Sinn Fein leader Gerry Adams will call on leaders of the U.S. Congress on Thursday to support efforts by Irish nationalists to maintain Northern Ireland’s place in the European Union after the rest of the United Kingdom leaves.

Sinn Fein president Gerry Adams speaks during an interview with Reuters at Government buildings in Dublin, Ireland March 9, 2017. REUTERS/Clodagh Kilcoyne

He was also set to ask the Irish government to resist any attempt by Britain to revert to ruling Northern Ireland directly from London for the first time in a decade, which he said would be “an enormous act of bad faith”.

Sinn Fein has led calls for Northern Ireland to be given a special status within the EU once the rest of the United Kingdom leaves, on the basis that 56 percent of voters in the province voted to remain in the Brexit referendum held last June.

Northern Ireland, the only part of the United Kingdom with a land border with the EU, is widely seen as the region most exposed to the economic and political fallout from Brexit.

Politicians from all sides have warned that the process of leaving the EU could increase tensions between mainly Catholic Irish nationalists who aspire to a united Ireland and predominantly Protestant pro-British Unionists. They do not, however, foresee a return to the violence that killed more than 3,600 people over three decades before a 1998 peace deal.

Both the British government and many pro-British unionists, who form a majority in Northern Ireland, have rejected the idea that parts of the United Kingdom could remain in the EU while other regions leave.

“The consequences of Brexit represents the biggest threat at this time to the wellbeing of the people of the island of Ireland,” Adams will say in a speech to the Congressional Friends of Ireland in Washington on Thursday.

“I presented the Congressional leaders with Sinn Fein’s proposal ‘The Case for the North to achieve Designated Special Status within the EU’,” he added, in remarks circulated in advance by Sinn Fein. “I asked the Congressional leaders to support this position.”

In the speech Adams will also warn the British government against replacing Northern Ireland’s devolved administration with direct rule.

Sinn Fein withdrew from Northern Ireland’s power-sharing government in January in protest at the handling of a scandal over the abuse of a heating subsidy scheme by its partner, the Democratic Unionist Party.

Following a hugely successful election for Sinn Fein, which left it just one seat behind the DUP and deprived unionists of their majority in the Northern Ireland assembly for the first time, the two parties are in talks to form a new government.

But Adams said the DUP did not appear close to meeting its demands for legal status for the Irish language and the creation of a Bill of Rights for the province, and that securing a deal would be “a challenge”.

If no deal is struck by March 27 the British Secretary of State for Northern Ireland, James Brokenshire, is obliged to call a fresh election but could also consider a temporary return to direct rule. He said in January he was not contemplating such a move.

“It has been suggested that British Direct Rule could be imposed if there is no agreement. This would be an enormous act of bad faith by London and a reversal of the joint position set out by the two governments (of Britain and Ireland) in 2006,” said Adams, who is a member of the Irish parliament in Dublin.

Reverting to Westminster rule would require legislation, which Adams described as “a very serious step which the Irish government would be compelled to oppose.”