TUV leader Jim Allister has written to the head of the Ulster Farmers' Union to express his "dismay" over its support for Theresa May's Brexit deal.
The North Antrim MLA slammed union officials for embracing what he described as a "disastrous" plan, which he said will "break-up the UK single market" on which farmers depend.
But the UFU hit back in a joint statement with the other major UK farming unions, saying leaving without a deal would "decimate our industry".
And the body representing Northern Ireland's hospitality industry has revealed the results of a poll of business owners, who have overwhelmingly backed Mrs May's deal.
In his letter to UFU president Ivor Ferguson, Mr Allister said the UFU's position "is beyond my powers of rationalisation".
He said: "Urging MPs to vote for an Irish Sea regulatory border is madness. Have you forgotten the business supply chain is a two way process and therefore, rushing to impede GB/NI trade is as dangerous as it is absurd?"
However, the bosses of the UK's four major farming unions show no sign of backing down. A joint statement on behalf of the UFU, NFU Scotland, NFU England and NFU Cymru, said: "We have argued for free and frictionless trade with the EU to continue, with no tariffs or non-tariff barriers.
"The default of trading with the EU under WTO rules alone is unacceptable and would decimate our industry.
"The draft Brexit Withdrawal Agreement, while not perfect, will ensure that there are no hard barriers on the day we leave the European Union, and will allow trade in agricultural goods and UK food & drink to continue throughout the transition period largely as before. This opportunity needs to be taken."
Yesterday, Hospitality Ulster published a poll indicating that three quarters of businesses it asked here in a survey supported the May deal. The industry body said: "The current draft agreement to exit the EU is far from perfect, and still causes some concern, but when faced with a no deal scenario, 74% of respondents to our industry poll support its acceptance, whilst recognising that further clarification on a number of issues is still required.
"We believe the current draft agreement is commercially better than a no deal scenario and will support the wider domestic economy on which our members depend, providing a framework for unfettered access to goods and services and visa free access for EU visitors to support the growing tourism market."