Cabinet Office minister Michael Gove is heading to Brussels at the start of a week of talks about the UK’s future relationship with the European Union.
Mr Gove will meet European Commission Vice President Maros Sefcovic to discuss implementation of the Brexit divorce deal.
And on Tuesday formal negotiations will resume as the two sides attempt to agree a post-Brexit trade deal.
Last week the UK said a lot of work remains before a deal can be reached.
An EU spokesman said their chief negotiator Michel Barnier was neither optimistic nor pessimistic but determined to reach a deal.
The Brexit transition period, in which the UK has kept to EU trading rules, ends on 31 December. The UK and EU are yet to agree a deal that will govern their future trade.
The last set of talks between the two sides ended acrimoniously when the UK government introduced the Internal Market Bill which would allow the UK to override parts of the original Brexit divorce deal – known as the withdrawal agreement.
Mr Sefcovic said that if the bill were to be adopted, it would constitute an “extremely serious violation” of the withdrawal agreement and of international law.
He urged the government to withdraw the bill “by the end of the month”, adding that the withdrawal agreement “contains a number of mechanisms and legal remedies to address violations of the legal obligations contained in the text – which the European Union will not be shy in using”.
The UK government said it would “discharge its treaty obligations in good faith”, but added that “it is important to remember the fundamental principle of parliamentary sovereignty.”
The bill has not been withdrawn and is set to be debated by MPs on Tuesday.