Boris Johnson has vowed to "do everything we need to do" - including an attempt to override post-Brexit arrangements with the EU - in order to "ensure there is no barrier down the Irish Sea".
Having held talks with Northern Ireland's First Minister Arlene Foster on Wednesday morning, the prime minister later raised the prospect of triggering Article 16 of the Northern Ireland Protocol.
It comes just days after the EU itself threatened - and then abandoned - to invoke Article 16 as part of its row with drugmakers over COVID vaccines.
The clause is intended to be used when the Protocol - designed to avoid a post-Brexit hard border on the island of Ireland and a key part of the UK's Withdrawal Agreement - is unexpectedly leading to serious "economic, societal or environmental difficulties".
It allows the UK or the EU to act unilaterally to avoid these difficulties.
Mr Johnson spoke in the House of Commons ahead of crunch talks later on Wednesday between Cabinet Office minister Michael Gove, European Commission vice-president Maros Sefcovic, Ms Foster and Northern Ireland's Deputy Minister Michelle O'Neill.
The prime minister told MPs: "I utterly share the frustrations... about the way the EU, in particular the EU Commission, temporarily seemed to call to use the Protocol in such a way as to impose a border contrary to the spirit of the Good Friday Agreement, contrary to the letter of the Good Friday Agreement.
"We will do everything we need to do, whether legislatively or indeed by invoking Article 16 of the Protocol to ensure there is no barrier down the Irish Sea."