Brexit Minister Lord Frost has said he is "concerned" by EU comments which suggests it does not want a "real negotiation" on Northern Ireland.
The UK wants fundamental changes to the NI Brexit deal known as the Protocol.
European Commission Vice-President Maros Sefcovic has said the EU is looking for further flexibilities but will not renegotiate.
Lord Frost said it would be a "significant mistake" to think the UK would not trigger Article 16.
That is the part of the Protocol which allows parts of the deal to be temporarily set aside if they are causing "serious economic, societal or environmental difficulties that are liable to persist, or to diversion of trade."
Lord Frost said the command paper he published in July sets out that the tests to use Article 16 are met.
'Take it or leave it?'
He told the House of Lords: "I urge the EU to take that judgement seriously.
"They would be making a significant mistake if they thought that we were not ready to use the Article 16 safeguards, if that were to be the only apparent way forward to deal with the situation in front of us.
"If we are to avoid Article 16, there must be a real negotiation between us and the EU.
"A real negotiation does not mean the EU coming up with its own plans for solutions, within the framework of the existing Protocol, and presenting them to us as "take it or leave it".
"I have been a bit concerned by a couple of the comments we have heard from Commission representatives in recent days which seem to suggest they might be considering this way forward."
He said officials had been going through the EU rule book with a "fine tooth comb" in an effort to come up with "creative and solid" ways to reduce the difficulties in moving goods from Great Britain to Northern Ireland.
It is understood there could be a unique agri-food deal for Northern Ireland as well as proposals on customs.
Germany's ambassador to the UK tweeted in response to Lord Frost's comments.
Seems we are entering a new phase with regard to the Northern Ireland protocol. Just as the EU becomes more pragmatic and understanding the UK adopts a less flexible line. Call that joint implementation. https://t.co/yVsgXUZz0B— Andreas Michaelis (@GermanAmbUK) September 13, 2021
Andreas Michaelis wrote: "Seems we are entering a new phase with regard to the Northern Ireland Protocol.
"Just as the EU becomes more pragmatic and understanding the UK adopts a less flexible line. Call that joint implementation."
However he made clear that the EU would not accept a UK demand that the European Court of Justice should be removed from the governance of the Protocol.
Lord Frost said he did not take Mr Sefcovic's comments about no renegotiation as a "dismissal" of the UK position but a 'fairly clear indication that there is more to be done.'
He declined to put a timescale on negotiations but said the matter was urgent.