The Prime Minister "shouldn't be surprised" that the DUP will not back his new deal, the party's Brexit spokesman has said.
Sammy Wilson claimed Boris Johnson had "not honoured the pledges" he made to the party within his departure agreement.
"It would disadvantage our economy quie seriously, and it is not in keeping with what the Prime Minister promised he would deliver: that the whole of the UK would leave the EU," he told talkRADIO's Julia Hartley-Brewer.
"He has not honoured the pledges he made to us. He sought flexibility from us, we gave him flexibility. The other side of the bargain was that Northern Ireland came out on the same terms as the rest of the UK. He didn't deliver on that."
Mr Wilson said as it stands, the deal - which will be voted on in the Commons on Saturday - would cause "all kinds of administrative and cashflow problems" for businesses in Northern Ireland.
Mr Johnson has just hours left to sell his deal to MPs before tomorrow's vote.
However, without the backing of the DUP, it is unclear whether it will pass through Parliament.
The Labour Party have also insisted they will not vote for the deal, although one Labour MP said there could be up to 20 party members willing to defy the whip.
It will be the first time the Commons has been sitting at a weekend for 37 years.