Brexit Secretary David Davis has criticised the "discourteous" European Union for publishing plans that would allow it to sanction the UK during a transition period.
Turning up the heat as a week of technical negotiations on the transition came to a close, Mr Davis said he regarded the Brussels documents as "political", published in bad faith, and "unwise".
The EU has released position papers showing it wants to put in place a method to rapidly curtail the UK's single market benefits if it breaches agreements on a transition deal.
Mr Davis said: "I do not think it was in good faith to publish a document with frankly discourteous language and actually implying that they could arbitrarily terminate in effect the implementation period.
"That's not what the aim of this exercise is, it's not in good faith, and we think it was unwise to publish that."
Under plans released by the European Commission, Brussels would be able to restrict the UK's access to the single market without going through the lengthy European Court of Justice (ECJ) legal process.
The position paper on transitional arrangements in the withdrawal agreement said there should be a "mechanism" allowing the EU to "suspend certain benefits" of single market membership during the transition period.
Such a move would be considered if referring the matter to the ECJ "would not bring in time the necessary remedies", according to the document, which sets out the EU's position on a transition deal in legal language.
On Wednesday, Stefaan De Rynck, an adviser to EU chief negotiator Michel Barnier, said sanctions for UK breaches of Brussels rules during the transition "of course" had to be part of any deal.
Mr Davis's comments came after a meeting of Theresa May's Brexit "war cabinet" which lasted a little over two hours on Thursday, during which senior ministers discussed what sort of future trade relationship they will seek with the EU.
Downing Street refused to comment on any details of the meeting.