The EU has threatened legal action if the UK proceeds with legislation that would undermine the Brexit Withdrawal Agreement.
The comment comes after a high-level meeting between officials from the EU and UK.
The meeting took place today in London between EU Commission Vice-President Maroš Šefčovič and UK Cabinet Office minister Michael Gove.
In a statement, the European Commission rejected the suggestion from Boris Johnson that his planned legislation is aimed at protecting the Good Friday Agreement, saying it would do the opposite.
It also said it wouldn't be shy in using legal remedies and action if the Withdrawal Agreement is breached.
It said that Mr Šefčovič "stated in no uncertain terms" that the implementation of the Withdrawal Agreement "is a legal obligation".
This includes the Protocol on Ireland/Northern Ireland which is an "essential part" of the deal.
Adoption of the UK's Internal Market Bill "would constitute an extremely serious violation of the Withdrawal Agreement and of international law", he said.
🇪🇺🇬🇧 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.
My statement following today's extraordinary Joint Committee on the #WithdrawalAgreement👇https://t.co/fiRyTxVNQD
— Maroš Šefčovič🇪🇺 (@MarosSefcovic) September 10, 2020
The statement added: "The European Union expects the letter and spirit of this Agreement to be fully respected. Violating the terms of the Withdrawal Agreement would break international law, undermine trust and put at risk the ongoing future relationship negotiations."
Mr Šefčovič called on the UK government to withdraw these measures from the draft Bill "in the shortest time possible and in any case by the end of the month".
He said that the UK had "seriously damaged trust between the EU and the UK" and that "it is now up to the UK government to re-establish that trust".
He added that the EU would "not be shy" in utilising legal remedies to address violations of the legal obligations contained in the Withdrawal Agreement.