The European Commission warned Thursday the British government "has seriously damaged trust between the EU and the UK" and demanded it abandon efforts to overwrite the Brexit withdrawal agreement.
Meanwhile in London talks, EU vice president Maros Sefcovic warned his British opposite number that unless the measures are withdrawn "by the end of the month" Brussels will consider taking legal action.
At a crisis meeting in London with minister Michael Gove, Sefcovic said: "if the bill were to be adopted, it would constitute an extremely serious violation of the Withdrawal Agreement and of international law."
In a statement issued after the meeting, he scorned London's argument that the bill -- which deals with UK internal market rules -- was designed to shore up peace in Northern Ireland.
"In fact," he said, Brussels "is of the view that it does the opposite."
"By putting forward this Bill, the UK has seriously damaged trust between the EU and the UK. It is now up to the UK government to re-establish that trust," the statement said.
"He reminded the UK government that the Withdrawal Agreement contains a number of mechanisms and legal remedies to address violations of the legal obligations contained in the text –- which the European Union will not be shy in using."
Diplomats in Brussels have already said the European Commission could complain to the European Court of Justice or activate an arbitration mechanism foreseen in the Withdrawal Agreement that Prime Minister Boris Johnson signed.