The UK has breached the deadline for responding to legal action by the European Commission over legislation that undermines the Northern Ireland Protocol.
The European Commission has said it has not yet received a response to the start of infringement proceedings, which were launched on 1 October.
The deadline for the UK to reply to the EU's letter of formal notice was 1 November.
The Internal Market Bill, which is currently going through the House of Lords, breaches elements of the Northern Ireland Protocol.
A spokesman for the EU's chief negotiator Michel Barnier said: "We sent a letter of formal notice on 1 October to the UK for breaching its obligations under the Withdrawal Agreement.
"As you know it had until the end of the month to submit its observations to that letter. To date I can confirm that the EU has received no reply from the UK. Therefore we are considering next steps, including issuing a reasoned opinion."
A "reasoned opinion" is the next stage in an infringement procedure taken by the European Commission.
Dan Ferrie added: "More generally I would recall the EU is fully committed to achieving the full, timely and effective implementation of the Withdrawal Agreement within the remaining time available. That's why we started the infringement procedure on 1 October.
"This dispute will have to be resolved."
Mr Ferrie said: "We are fully dedicated to the full implementation of the Withdrawal Agreement.
"That is an agreement we reached with the UK in order to avoid a hard border on the island of Ireland, in order to protect peace and stability on the island of Ireland. That agreement needs to be fully implemented and ready to go on January 1.
"We will be expecting a response from the UK and in the meantime we will be considering our next steps."
The Internal Market Bill would give UK ministers the power to unilaterally decide on aspects of the Northern Ireland Protocol, a key part of the Withdrawal Agreement, including the issues of tariffs on goods moving from Britain to Northern Ireland, and on the issue of how EU state aid rules will apply.
Progress on Brexit level playing field, far from concluded - Coveney
Minister for Foreign Affairs Simon Coveney has said that some progress has been made in trade talks on the so-called level playing field but agreement on one of the most persistent areas of disagreement was far from concluded.
"If there is not a basic set of rules around fair competition that both sides commit to complying with and if there is not a governance structure that can deal with disputes, then in my view there will not be a trade deal," he told an online conference.
"My understanding is there is some progress being made in this area but it's far from concluded yet," Mr Coveney said, adding that he was confident a deal could be reached but that time may run out to strike one.