A former US Special Envoy to Northern Ireland says the British government is putting the Irish border at risk over chilled meats.
Mick Mulvaney was speaking as London is bringing forward legislation that would override aspects of the Brexit agreement between the EU and UK.
The DUP is refusing to re-enter the assembly at Stormont until the Northern Ireland Protocol is torn up.
While some 60% of MLAs elected to the assembly are in favour of the protocol.
Mr Mulvaney told The Hard Shoulder the Good Friday Agreement is being put in jeopardy for the sake of very small economic gains.
"If you and I have an agreement - and you and I have an agreement with somebody else - and one of the parties decides they want to unilaterally change things, that sort of makes you wonder if you had an agreement in the first place.
"And it certainly makes it more difficult to have agreements in the future.
"We were excited when the Northern Ireland Protocol got agreed to, because it was an agreement.
"We'd love to see that same sense of negotiation carry through here.
"There are some important things here philosophically, I get that - there's some critical things here historically, I get that.
"But economically, the amount of goods flowing from Great Britain to Northern Ireland and into the Republic is so small.
"It's got Americans scratching their heads going 'Do we really want to put the Good Friday/Belfast Agreements, the lack of a hard border, at risk over chilled meats?"
'The bona fides count'
He says Britain will have difficulty making an agreement with other nations, such as the United States.
"That's not a very good base from which to work.
"The relationship between the US and UK is very strong, obviously between the US and Ireland is very strong as well, but when we start talking about things like free trade agreements the credibility and the bona fides count.
"You have to be able to sit down and trust the people you're speaking with.
"And everytime you unilaterally change an agreement, it erodes that".
Mr Mulvaney says if the situation is managed correctly by all sides, "Northern Ireland will be the only place in the whole world that will have complete access to the United Kingdom market and complete access to the EU.
"That's a tremendous opportunity, that's something that people should be working towards and seeking to take advantage of - not looking for ways to blow up or to interfere with".
He adds that he hopes "cool heads continue to prevail, and that discussions continue".
Mr Mulvaney was appointed by former US President Donald Trump, and resigned his post in protest at the riots in Washington DC last January.