Colum Eastwood said the controversial piece of legislation “rides a coach and horses through the Good Friday Agreement”, and told the Government that if they tampered with the peace accord, “there will be no trade deal”.
That has been echoed by Democratic US Presidential candidate Joe Biden and Nancy Pelosi, speaker of the US Congress.
The Foyle MP added that having no border in Ireland was paramount to securing a trade deal with the US, and that if this condition was not met, an agreement “will not be accepted by anybody at the height of power” on the other side of the Atlantic.
His warning came as International Trade Secretary Liz Truss denied that trade discussions with the US had come to a halt on Monday.
Raising his concerns over changes to the Brexit deal in the House of Commons, Mr Eastwood said members of the US Congress were “saying there will not be a trade deal between the US and this country if you do any damage to the protocol or the Good Friday Agreement. That is what they’ve said. People should listen.”
Intervening, DUP MP Sammy Wilson said: “I must say that I am absolutely amazed at the comments which he has made.
“Because of course, he will know that our biggest trading partner outside Great Britain is the United States of America, so any trade deal with America is bound to have a beneficial impact on the people of Northern Ireland and on the economy of Northern Ireland.
“Is he telling me and this House that his party will actively campaign against a trade deal with America which would benefit his constituents, my constituents and the Northern Ireland economy?”
Mr Eastwood replied: “We want a trade deal and we want to be able to trade right around the world, but the warning is clear: if you mess about with the Good Friday Agreement and all of our political progress, there will be no trade deal.”
Foreign Secretary Dominic Raab, who is in Washington for talks, told US congressional leaders yesterday that the “politicisation” of Northern Ireland issues by Brussels in the Brexit trade talks was threatening the Good Friday Agreement.
Mr Raab said he had made clear the UK’s “absolute” commitment to the peace deal.