The European Commission launched two new legal proceedings against Britain on Wednesday after London published plans to override some post-Brexit rules governing Northern Irish trade, and resumed another challenge it had previously paused.
The proceedings could result in fines imposed by the European Court of Justice, although these would likely be more than a year away.
The Commission, which oversees relations with former EU member Britain for the 27-member European Union, said it still wanted to resume talks with Britain to resolve difficulties in shipping British products to Northern Ireland.
The British province is in the EU single market for goods, meaning imports from the rest of the United Kingdom are subject to customs declarations and sometimes require checks on their arrival. The arrangement was set to avoid reinstating border controls between Northern Ireland and EU member Ireland, which were dropped after the 1998 Good Friday peace agreement.
"The British government has once again announced its intention to break international law," an EU official said. "We don't think it takes a lawyer to know that unilaterally changing an agreement is wrong."