• The Internal Market Bill throws out some provisions designed to keep the border between Northern Ireland and the Irish Republic open
  • Supporters say the measure would prevent the imposition of damaging tariffs on goods shipped from Northern Ireland to England, Scotland and Wales
  • The EU sent a letter of formal notice and could escalate the confrontation to the European Court of Justice

The European Union on Thursday initiated legal action against British Prime Minister Boris Johnson’s effort to rewrite the Brexit withdrawal agreement after he refused to revise a measure in Parliament that undermines a deal involving Northern Ireland approved last year.

The EU sent a letter of formal notice that could lead to a confrontation in the European Court of Justice after the deadline for revising the U.K.’s Internal Market Bill expired Wednesday.

The bill, already approved by the House of Commons, reneges on promises not to create border issues between the Republic of Ireland and Northern Ireland. The measure now is before the House of Lords. Supporters say it would prevent damaging tariffs on goods shipped from Northern Ireland to England, Wales and Scotland.

European Commission President Ursula von der Leyen said the measure is in “full contradiction” of earlier guarantees and constitutes a breach of good faith.

Johnson’s government has a month to reply as negotiations on an overall trade deal continue. The U.K.’s transition period ends Dec. 31 and Johnson has pledged to exit the EU whether or not a permanent trade deal is in place. The EU has said it would not sign off on any deal as long as the market bill remains intact.

Brandon Lewis, Johnson’s minister for Northern Ireland, has acknowledged the measure violates international law but called the breach minor.

The bill would eliminate requirements for inspections and paperwork for shipments from Northern Ireland across the Irish Sea. It also allows Britain independence in setting levels of state aid to certain sectors of the province’s economy. A spokesman for Johnson told the Washington Post the bill would protect trade within the U.K.

Johnson called the agreement on Northern Ireland signed last year flawed after initially hailing it as a breakthrough. The agreement required Northern Ireland to continue to enforce EU rules on customs duties, and health and product standards so the border with the Irish Republic could remain open.