An extended transition period would not solve a fundamental problem with the EU’s backstop proposals, the DUP said.
The UK would continue to pay contributions to the bloc while having no say post-Brexit, deputy leader Nigel Dodds warned.
He said: “Such an extension would cost United Kingdom billions of pounds, yet our fundamental problem with the EU proposal remains.”
He repeated his party’s criticisms of the EU’s Irish border backstop position.
“I am glad that it is not just unionists in Northern Ireland who recognise the dangers of the EU proposals on the backstop to the Union.
“Such a backstop is unacceptable to many others from right across the United Kingdom.”
Meanwhile, his Sinn Fein counterpart Michelle O’Neill said Prime Minister Theresa May had refused to hold a joint meeting with the leaders of Northern Ireland’s main anti-Brexit parties.
She said Mrs May had turned down a request for talks with the leaders of Sinn Fein, the nationalist SDLP, cross-community Alliance Party and the Green Party in Northern Ireland.
Mrs O’Neill said: “In order to preserve her toxic alliance with the DUP, she is trampling over the rights of citizens by acquiescing to that party’s refusal to share power (at Stormont) on the basis of equality.
“And by refusing to meet their representatives, Theresa May is also ignoring the democratic will of the majority in the north who voted to reject Brexit.”
She said the British Government was incapable of acting responsibly or with any semblance of impartiality while it remained wedded to the DUP.
“Theresa May is showing nothing but disdain for the people of the north, for the Good Friday Agreement, for our economy and rights and for the peace process.
“It is an appalling failure of her responsibilities as a co-equal guarantor of our peace and political process and there is an onus on the Irish Government and EU27 to defend our best interests during this critical stage of the Brexit negotiations.”