The government has “seriously broken” its commitment to the Democratic Unionist party, which forced its MPs to vote with Labour, one of its senior MPs has said, throwing the future of Theresa May’s government into further doubt.

Sammy Wilson, the party’s Brexit spokesman, said the government had not stuck to its promise that Northern Ireland would not be treated differently from the rest of the UK in the Brexit withdrawal agreement.

“Since the government has not honoured its side of the bargain we tonight tried to spell out some of the consequences of that,” Wilson told the BBC.

The DUP, whose 10 votes May relies on for a majority in parliament, abstained or backed Labour in a series of votes on the budget.

The DUP’s fury about the prime minister’s Brexit deal, and its decision to withhold support from the finance bill raised doubts about the future of the confidence and supply arrangement on which May’s ability to secure a majority is based.

Wilson, said the government had reneged on its promises, and “consequences were inevitable”.

“The prime minister has undermined her own authority with her own party and with our party by blatantly breaking promises about what she would deliver in the Brexit deal with the European Union,” he said.

The prime minister turned to the DUP in June last year when her majority was wiped out in the general election.

The Government made clear commitments never to undermine the constitutional or economic integrity of the United Kingdom. They have reneged. Consequences were inevitable. pic.twitter.com/I9OB2tzn2o — Sammy Wilson MP (@eastantrimmp) November 19, 2018

The agreement the two parties subsequently signed, and which led to more than £1bn of extra resources being directed to Northern Ireland, said the DUP would support the government on “all motions of confidence; and on the Queen’s speech; the budget; finance bills; money bills, supply and appropriation legislation and estimates”.

After it emerged that the DUP had abandoned the Conservatives on a series of issues, including a Labour motion on child poverty, Jon Trickett, the shadow minister for the Cabinet Office, said: “We no longer have a functioning government. With Brexit only a few months away, something has got to give.”

DUP sources suggested the decision to withhold their support was a shot across the bows of the government, rather than a signal that the confidence and supply deal was in abeyance.

“None of the [amendments] have financial consequences,” Wilson said. “All of them were designed to send a political message to the government.”

None of the opposition amendments passed and the DUP could still opt to support the budget at later stages of the legislative process. But, without the DUP’s support, May would find passing any contentious legislation in the coming weeks impossible, and the gesture underlined the depth of the party’s frustrations about the outcome of the Brexit negotiations.

Arlene Foster’s party has pledged to vote against May’s deal when she brings it back to the House of Commons, which is likely to be early next month.

The DUP objects in particular to the Irish backstop, which it argues would keep Northern Ireland in the regulatory orbit of the EU – and in a different regime to the rest of the UK.

The government had to cave in on the issue of cutting the stakes for addictive fixed-odds betting machines, which prompted the resignation of the sports minister Tracey Crouch, after the threat of a backbench revolt on the finance bill.

In a fresh concession on Monday night, the Treasury minister, Robert Jenrick, announced that the government would publish economic analysis of remaining in the EU, alongside its projections for the government’s Brexit deal, before MPs vote on it.

Jenrick’s concession, made during the debate, came after a cross-party amendment tabled by Labour’s Chuka Umunna and the Conservative Anna Soubry, secured the backing of 11 Conservative MPs – more than enough to wipe out May’s majority, even without DUP backing.