Boris Johnson should again seek to re-negotiate the Brexit deal if he wants DUP support, Arlene Foster has said.
The DUP leader told the party’s conference that the DUP had sent the PM to the “naughty step in Parliament” twice in the last week.
The DUP has twice voted against the government on crucial Brexit votes recently, because of its opposition to Mr Johnson’s Brexit strategy.
The party said it would not support the NI arrangements negotiated by the PM.
This is because it “creates a border in the Irish Sea”.
The DUP leader told Saturday’s annual conference she would encourage the PM to seek further changes to the deal.
“We will not give support to the government when we believe they are fundamentally wrong,” she said.
Boris Johnson does not have a Conservative majority in Parliament and the DUP’s votes hold the balance of power on key decisions in the Commons.
Detrimental to Northern Ireland
Mrs Foster accused Number 10 of acting in a way that was “detrimental” to Northern Ireland and was taking the country in the wrong direction.
She also said if the government did not change its strategy that the DUP’s 10 MPs would “oppose them and we will use our votes to defeat them”.
On Monday, the government will ask MPs to vote in favour of its call for a general election.
Mrs Foster did not say whether the party would vote with the government, but said the DUP was “ready for any general election that may come”.
The DUP leader also addressed the Stormont deadlock.
Northern Ireland has been without a government since 2017, when the two main power-sharing parties split in a bitter row.
One of the key sticking points has been the demand from Sinn Fein to legislate for an Irish language act, with the DUP refusing to agree to it.
Mrs Foster said her party remained committed to “legislate in a balanced way for language and culture”.
“If we can find a way to craft language and culture laws that facilitates those who speak the language, but does not inappropriately infringe on or threaten others, the DUP will not be found wanting,” she added.
“But overall agreement needs to be a two-way street.”
Speaking earlier, Nigel Dodds told the conference that the union of the United Kingdom was “non-negotiable” in any Brexit deal.
The party has said it will not support the Brexit arrangements for Northern Ireland negotiated by Boris Johnson as it “creates a border in the Irish Sea”.
The DUP deputy leader urged the prime minister to stick to commitments he made last year, when he said no Conservative government would support such a plan.
The party argued the deal would damage the local economy and undermine the union.
“I say it again clearly for those who have failed to listen… the union of this United Kingdom is non-negotiable,” said Mr Dodds.
At last year’s conference, Boris Johnson was the keynote speaker.
He told DUP members that no Conservative government should support a plan that would lead to differences between Northern Ireland and the rest of the UK.
‘The pressures will be great’
Mr Dodds accused Mr Johnson and other government ministers of not knowing “what on earth” they had negotiated as part of the revised withdrawal agreement with the EU.
He said the plan, which would see NI businesses having to fill in exit declaration forms on goods going to GB, new checks on goods crossing the Irish Sea and extra administration, as “the worst of all worlds”.
The North Belfast MP also said the DUP would not back down from opposing the deal.
“The coming days will not be easy, the pressures will be great,” he added.
Analysis by BBC News NI Political Reporter, Jayne McCormack
There was a more muted feel at this year’s DUP conference, with no star turn from Boris Johnson.
Instead the party’s leadership took turns to chastise him for reneging on Brexit commitments he made when he stood on that very stage last November.
Both Arlene Foster and Nigel Dodds seemed angry and emotional during their speeches – as many DUP politicians have sounded in recent days.
Just like last year when it opposed Theresa May’s Brexit deal, the DUP is again in a political corner.
But this time, it does not have the ear of many Conservative Brexiteer MPs, who have sided with Boris Johnson and will likely dismiss the DUP’s demands.
The DUP has said it will wait until Monday before giving its response to Mr Johnson’s call for a general election.
The prime minister wants Westminster parties to agree to an election on 12 December.
The DUP entered a confidence and supply arrangement with the Conservative Party almost two and half years ago and helped prop up the minority government under Mr Johnson’s predecessor, Theresa May.
The DUP has met Mr Johnson many times since he became prime minister.
At the start of this month, DUP members chanted his name when he addressed their fringe event at the Conservative Party’s annual conference in Manchester.
But the relationship soured on 17 October, when Mr Johnson struck a Brexit deal with EU leaders that the DUP said it could not endorse.
All Northern Ireland MPs who take their seats in the Commons – the 10 DUP representatives and independent North Down MP Lady Hermon – opposed the government in votes over the EU withdrawal deal and an accelerated timetable to fast-track the bill through Parliament.