EU Commissioner Phil Hogan has said the UK's no-deal tariff plans - proposals that would see no import duties levied on goods entering Northern Ireland across the border - are likely to breach World Trade Organization rules.
Mr Hogan, who is commissioner for agriculture and rural development, claimed the plans announced by Whitehall this week were "political" and designed to "change in the news cycle from the political chaos on London".
"I think they are incompatible with WTO rules," he said of the plans, after arriving at an agriculture conference in Dublin.
Mr Hogan added: "I think the timing of it was unfortunate and it was a deliberate attempt to put Ireland more on the agenda, as if it wasn't on the agenda already."
Mr Hogan said there were "no more excuses" for Westminster not to ratify the deal.
He noted that "intensive discussions" were taking place with the UK Government and the DUP and some Brexiteers.
"They do realise they are risking a no-deal but also a no Brexit, and I think that's concentrating their minds," he said.
"I hope she (Theresa May) is successful in getting some deal because the deal is on the table from the European Union side with the UK since the 25th of November. All the clarifications that were needed were given in a very open and generous way by the European Union last Monday - there's no more excuses."
Mr Hogan said MPs in Westminster were behaving in an unacceptable way.
"They have had a long time to do all of this up until now and leaving it until the 11th hour is creating instability and uncertainty for their own people, but also for Irish people and for the European Union generally," he said.
"That is certainly not an acceptable way of political behaviour from the mother of parliaments."
He said he would not pre-judge whether European leaders would be prepared to offer Mrs May a Brexit extension.
Mr Hogan said the EU stood ready to support Irish farmers who might be adversely impacted by Brexit.
But he urged those in the sector to "remain calm" until the final shape of Brexit was clear.
"We are well advanced for all scenarios including very difficult situations for farmers in Europe generally and indeed for Irish farmers because we are very exposed, particularly in the beef sector," he said.
He added: "The European Union is ready to help them at the appropriate time when we see what the conclusions of the negotiations in London are."
Mr Hogan said there was not yet a market crisis - characterising the situation as only a "political crisis".
He said Irish farmers had weathered previous troubled periods, such as mad cow and foot and mouth diseases, with EU help.
"We shouldn't talk ourselves into a crisis," he added.