House Speaker Nancy Pelosi Nancy PelosiHoyer: House should vote on COVID-19 aid — with or without a bipartisan deal Ruth Bader Ginsburg lies in repose at Supreme Court McCarthy threatens motion to oust Pelosi if she moves forward with impeachment MORE (D-Calif.) warned British politicians negotiating a withdrawal from the European Union that a trade deal with the U.S. would be off the table if Brexit harms Irish peace.

“Let me be clear: if the Brexit deal undermines the Good Friday accords, there will be no chance of a U.S.-U.K. trade agreement,” Pelosi said in a Wednesday address to the Irish Parliament.

The 1998 Good Friday Agreement brought to an end the Northern Ireland conflict, which broke out in the 1960s.

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One of the central difficulties British negotiators have faced in their Brexit negotiations is how to deal with Northern Ireland, which is part of the U.K. but shares a border with Ireland, which is part of the EU.

Those opposed to Brexit have raised concerns that a Brexit deal might require imposing a hard border between Northern Ireland and Ireland, upsetting the deal that has maintained peace for over two decades.

British Prime Minister Theresa May Theresa Mary MayAre US-Japan relations on the rocks? Trump insulted UK's May, called Germany's Merkel 'stupid' in calls: report Bolton says Boris Johnson is 'playing Trump like a fiddle' MORE’s Brexit proposal, called for an “Irish backstop” that would essentially leave the U.K. in Europe’s customs union and single market unless an alternative solution was agreed upon for Northern Ireland. Britain’s Parliament rejected the plan on several occasions, with Brexit proponents arguing that it left the U.K. confined to the EU system of trade and rules while stripping it of any political power within the trading bloc.

Pelosi’s words add pressure to Brexiteers, warning that the U.S. will not be quick to rebuild its trade relationship with a post-Europe Britain in the event that Brexit results in an Irish border.

"We must ensure that nothing happens in Brexit discussions that imperils the Good Friday accord — including, but not limited to, the seamless border between the Irish Republic and Northern Ireland," Pelosi said in her Wednesday address.

Because the U.S. trade relationship with Britain is largely governed through trade deals with the EU, Britain would need to lay out a new trade deal with the U.S. following Brexit.

Any new trade deal would have to be brought to a vote in Congress, meaning the Speaker could block a vote.