DUP leader Arlene Foster has repeated her criticism of the Northern Ireland backstop ahead of Westminster’s vote on the prime minister’s proposed EU Withdrawal Agreement.
MPs will vote on the deal on Tuesday after two days of final debate.
The government has urged Parliament to back the deal.
However, the DUP’s 10 MPs are expected to vote against the deal over their opposition to the backstop.
It is expected that about 100 Conservative MPs will join Labour and other opposition parties in voting against the deal.
The backstop, a mechanism that is included in the withdrawal agreement, is an insurance policy designed to avoid a hard Irish border, if another solution is not found through a wider UK-EU trade deal.
Mrs Foster has vocally opposed the backstop and renewed her assault on Monday.
She said her party wanted a “sensible deal” between the UK and the EU but that the current withdrawal agreement “is not that deal”.
“Principally, it is flawed because of the backstop,” she added.
Mrs Foster said the backstop “fundamentally undermines Northern Ireland’s place in the UK” and “runs roughshod” over the principle of consent contained in the Good Friday Agreement.
While the DUP will vote against the deal, it will almost certainly back the prime minister if a no confidence motion is brought against her in Parliament.
Labour leader Jeremy Corbyn has vowed to table such a motion if the deal is defeated on Tuesday.