Mrs Haley, in a speech in London, lambasted Democrats in the US for trying to undermine Britain’s attempts to overhaul the protocol.
Mrs Haley told the Policy Exchange think tank: “In terms of the Northern Ireland Protocol, I know that some of the politicians in America have decided to weigh in on that. It’s none of their business.
“This is something that you have to decide, this is something that has to be in the best interest of your people, and you’ve got to decide what’s going to make you strong in the end. I just don’t think it’s our place to be weighing in on this at all.”
The former governor of South Carolina said she supported Brexit and watched it unfold with “bated breath because I love when people use the power of their voice.”
She added: “The fact that they [the British people] wanted to leave the EU, I don’t blame them. I saw at the United Nations what the EU does. It makes all these countries do what they want them to do and not what’s in their best interest.”