The European Union has launched legal action against the United Kingdom after Prime Minister Boris Johnson failed to respond to its demand that he drop legislation that would override the withdrawal agreement and break international law, The Guardian reported on Thursday. European Commission President Ursula von der Leyen made the announcement.

Johnson had tabled an Internal Market Bill last month that was the cause of problems between Britain and the EU. The trading bloc gave Johnson until the end of September to drop contentious clauses in the legislation.

Under the Internal Market Bill, British ministers would be able to decide whether to notify the European Commission of any government subsidy decisions that could affect goods trade in Northern Ireland. They will also be able to decide on waiver of export summary declarations export while sending goods from Northern Ireland to the rest of the UK. The British government had said that the legislation was required as a “safety net” for the UK market in case the European Union acted unreasonably.

“We had invited our British friends to remove the problematic parts of their draft internal market bill by the end of September,” von der Leyen said. “This draft bill is, by its very nature, a breach of the obligation of good faith laid down in the withdrawal agreement. Moreover, if adopted as is, it will be in full contradiction to the protocol on Ireland and Northern Ireland.” Von der Leyen said that since the problematic provisions were not removed, the United Kingdom was issued a notice on Thursday.

An unidentified spokesperson for British government told The Guardian that the government will respond to the notice “in due course”. The matter could be heard by the European Court of Justice. In that case, Britain will have to abide by its ruling, as it is bound by decisions of cases that begin before the end of the transition period on December 31, and for four years thereafter.

Britain formally exited the EU on January 31 this year. The country has to reach a trade deal with the bloc by the end of its transition period on December 31. If it fails to do so, it may be subjected to tariffs and economic hurdles in 2021. The negotiations between the two sides have primarily been delayed due to disagreements over fair competition rules and fishing rights.

On September 7, Boris Johnson set an October 15 deadline for a post-Brexit trade agreement with the European Union, and warned that he could walk away from the negotiations if a deal is not reached by that date. The talks between the UK and the EU are still under way.