The European Commission has filed a case against the U.K. at the Court of Justice of the EU (ECJ) for failing to uphold terms of the Brexit agreement, specifically regarding the free movement of people. The dispute focuses on Britain’s non-compliance with the rights of EU nationals residing in the U.K. under the Brexit deal.

The deal, signed in 2020, allowed EU citizens and their families living in the U.K. to remain and granted Brits similar rights to live, work, and study in the EU. However, the Commission claims that the U.K. has not properly implemented these rights, particularly for workers and extended family members of EU nationals.

The violations occurred in late 2020, before the final Brexit trade agreement was signed. A U.K. government spokesperson pointed out that the issues stem from the transition period when the country was still an EU member, and emphasized that the government is focused on resetting relations with the EU.

The case marks the first major legal confrontation since Keir Starmer’s Labour government took power. Pro-Brexit politicians, including former Home Secretary Priti Patel, have criticized the EU’s actions, warning that it may signal attempts to reintegrate the U.K. under EU jurisdiction. The British government has vowed to defend the case vigorously.