LONDON (Reuters) - The DUP, the Northern Irish unionist party that props up Theresa May’s government, could vote against this month’s UK budget if the prime minister breaches the party’s red lines over Brexit at an EU summit, the BBC and Sky News said on Wednesday.

Northern Irish Democratic Unionist Party (DUP) leader Arlene Foster holds a news conference at the European Parliament after a meeting with EUÕs Brexit negotiator Michel Barnier in Brussels October 9, 2018. REUTERS/Yves Herman

May relies on the support of the Democratic Unionist Party on major votes after she lost her governing Conservative Party’s majority at an election last year.

Budget votes have traditionally been seen as votes of confidence, but asked whether that was the case, May’s spokesman said: “The answer to that factually is no” and cited legislation which sets out the conditions for calling an election.

Just six months before Britain is due to leave the European Union, May’s negotiations with the bloc are under scrutiny from all sides of the Brexit debate, with the DUP concerned that any deal may effectively split Northern Ireland from the mainland.

Both Britain and the EU had hoped to strike a deal on a withdrawal agreement at a summit on Wednesday and Thursday next week, but May’s Brexit spokesman has said that London is now looking for progress to be made at the meeting.

The BBC and Sky, without citing sources, reported that the DUP could vote against the budget on Oct. 29 if a deal meant new barriers between the British province and the rest of the United Kingdom.

A DUP source said it was “unacceptable that we would be treated differently to the rest of the UK ... We will not be bounced into anything.”

On Tuesday, Nigel Dodds, deputy leader of the DUP, warned the government not to repeat “that mistake” from December - when the party almost pulled the rug out from an interim accord with the EU by scuppering a proposal on regulatory alignment between the bloc and the province.

DUP leader Arlene Foster has said there is “only one red line” in the Brexit talks, ruling out her party’s support for any arrangement “which could give rise to either customs or regulatory barriers within the UK internal market”.

May and her Brexit minister Dominic Raab have repeatedly said Britain cannot accept any deal that fails to protect the integrity of Britain.