DUP members have been told that the party's recent local election result was a renewed mandate to continue opposing post-Brexit trade arrangements.
The comments by party leader Jeffrey Donaldson in a letter to newly elected councillors comes amid growing speculation that the DUP may be planning to end their boycott of Stormont over the Northern Ireland Protocol.
The unionist party has been involved in talks with the British government in recent weeks about the potential return of devolution although Mr Donaldson has insisted that his party’s requirements for returning to the executive have yet to be met.
In his letter to 122 recently elected councillors Mr Donaldson wrote: "Last Thursday our mandate was renewed, and we were able to reaffirm our contract with the people to fully restore Northern Ireland's position in the United Kingdom.
"Whilst the non-unionist commentators seek to pick holes in our mandate, I am heartened that we were able to increase our vote share from the NI Assembly election last year."
Mr Donaldson outlined his continued opposition to the protocol.
"The Northern Ireland Protocol placed a barrier between us and the rest of the United Kingdom which is offensive to us as unionists," he said.
"Indeed, whilst nationalists seek to play down the impact of the Irish Sea border, we should all remember that Sinn Féin and SDLP politicians were in uproar at the very idea of any additional cameras being placed on the north-south border."
He added that future progress may be difficult.
"Northern Ireland will struggle to move forward if republicans have so little respect for their unionist neighbours that they can't see the problem with the current protocol arrangements," he said.
"I would never have expected nor asked my nationalist neighbours to accept the kind of infrastructure north-south that we are being asked to accept east-west."
