Any attempt to roll back rules governing the UK’s post-Brexit trade with Northern Ireland could hurt chances of a bilateral trade agreement with the US, the White House said Wednesday. 

White House Press Secretary Karine Jean-Pierre said there is “no formal linkage” between the two issues but warned new British Prime Minister Liz Truss’s government against such a move.

“Efforts to undo the Northern Ireland protocol would not create a a conducive environment, and so that’s basically where we are with the dialogue,” Jean-Pierre told reporters.

There are worries that Truss, a Conservative, could undo parts of the Brexit deal that keeps Northern Ireland in the bloc’s single market for goods to avoid a hard border on the island of Ireland. A stand-off over this has strained relations between the European Union and the UK, raising the prospect of a trade war if the British government negates the rules.

President Joe Biden spoke with Truss by phone Tuesday after she became prime minister, and the two leaders discussed “the importance of reaching a negotiated agreement with the European Union on the Northern Ireland protocol,” the White House said.