Northern Ireland's two largest unionist parties have clashed over the DUP's decision to voice support for Boris Johnson's Brexit proposals.
UUP MLA Doug Beattie is the latest unionist to criticise the party, saying that they have done a "u-turn on a border in the Irish sea".
Mr Beattie said that the party's stance will cause economic and constitutional damage to Northern Ireland and the United Kingdom.
His comments come after party grandee Lord Empey questioned how any unionist could give their support to the Prime Minister's proposed deal.
However, DUP MP Sir Jeffrey Donaldson has rejected the criticism, saying the proposals will not create a trade barrier in the Irish Sea.
"It’s easy to sit on the sidelines and complain without offering a single realistic solution," the former UUP MLA said.
Sir Jeffrey accused Lord Empey of "fighting battles against the DUP which he lost fifteen years ago" and said that unionist voters want their leaders to work together.
"He should deal with his bitterness, focus on the policy rather than the person and move on," the DUP MP said.
He said that the PM's deal "removes the threat of the backstop and fully respects our constitutional position within the UK".
"Sinn Fein and Dublin know it and that is why they have expressed their opposition to this deal with so much anger," the Lagan Valley MP said.
Sir Jeffrey said that the UUP had achieved "absolutely nothing" in their past attempts to work with the Conservative Party.
"The DUP sought and won the commitment in the PM’s proposals for the prior and ongoing consent of the Executive and the Assembly to any regulatory divergence between Northern Ireland and the rest of the United Kingdom," he said.
The MP said that the UK as a whole is leaving the EU single market and that any remaining regulatory alignment with the EU would only apply to goods such as agri-food to appease Northern Ireland's farmers and the business community.
"The DUP is absolutely clear that an all-Ireland economic zone, with all goods and services exclusively under EU rules, and the resulting regulatory border in the Irish Sea is not something we would support," Sir Jeffrey said.
"Nor will we support trade barriers between Northern Ireland and Great Britain and that is why this deal means Northern Ireland will remain firmly within the U.K. customs arrangements and outside the EU customs union."
Sir Jeffrey said that it made sense for Northern Ireland to have distinct arrangements in cases like the Single Electricity Market which is "economically beneficial".
He said that Mr Johnson recognised that the backstop "risked weakening the Belfast Agreement" and that consent from both nationalists and unionists would be needed to reach agreement.
"That of course remains our position. This is fundamental to democratic accountability and our place in the Union and all unionists should be supporting the Prime Minister in his stance.”
Upper Bann MLA Doug Beattie accused the DUP of "making it up as they go along", citing comments from party leader Arlene Foster that Northern Ireland's MP may get a say on Brexit arrangements if Stormont does not reconvene.
“These proposals, and the uncertainty which they bring, will cause constitutional and economic damage to Northern Ireland," the former British soldier said.
"Not only have the DUP done a complete U-turn on a border in the Irish Sea, but Northern Ireland will still come under the jurisdiction of EU Courts while the rest of the UK moves on. The DUP repeatedly claimed the UK would leave the EU as one nation in the same way we joined.
"This deal separates and segregates Northern Ireland from the rest of the UK as we would leave under different terms."
Mr Beattie accused the DUP of trying to "district from another slew of broken promises".
“The DUP claimed that they had power and influence in Westminster. But with that comes responsibility and it is they who are responsible for putting a border in the Irish Sea.
"It is feeble and pathetic of them to try and portray others as having responsibility for the DUP’s decision to put a border in the Irish Sea, undermining the economic and constitutional integrity of the United Kingdom.”