The US President Donald Trump claims the Brexit deal could mean his country cannot trade with Britain.
Speaking to reporters before a trip to Mississippi, he said: "I think we have to take a look at seriously whether or not the UK is allowed to trade because you know right now, if you look at the deal they may not be able to trade with us".
"That wouldn't be a good thing. I don't think they meant that, I don't think the (British) prime minister meant that and hopefully she'll be able to do something about that but right now as the deal stands they may not be able to trade with the US and I don't think they want that at all, that would be a very big negative for the deal."
However Downing Street disputes his comments.
A spokesperson for British Prime Minister Theresa May insists the UK would be able to trade with countries around the world - including America.
She faces a fight to get her deal through the British House of Commons.
She's visiting Northern Ireland today as she continues her attempts to sell the agreement.
She'll meet students academics and community leaders at an event at Queens University.
She is also due to travel to Wales.