MADRID (Reuters) - Spain’s minority Socialist government plans to announce an early general election after its expected defeat in a budget vote on Wednesday following its refusal to negotiate Catalan self-determination, political sources said on Tuesday.

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Two small Catalan pro-independence parties, on whose votes the government has been relying to pass legislation, have so far maintained their blanket rejection of the budget.

They said they were open to negotiate until the budget vote if the government promised them a dialogue on the right to self-determination, but that right is prohibited by the Spanish constitution.

Budget Minister Maria Jesus Montero told parliament the government would “not give in to blackmail” over the budget.

“If you want self-determination, I can tell you that there will be no budget,” she said, warning that Catalonia would lose what she called a good, generous budget for the region.

The government and Socialist party sources said the snap election date had not been set, although April 14 was most likely, followed by April 28, because Prime Minister Pedro Sanchez wants a ballot as soon as possible to mobilize left-leaning voters against the threat of the right coming to power.

The Socialists are ahead in opinion polls which show them on around 30 percent of voting intentions, but the two main right-of-center parties together poll at more than 30 percent. In Spain’s most populous region of Andalusia they unseated the Socialists last year with the help of the far-right party Vox.

“The idea is to announce we’re calling elections as soon as possible once the (vote on) the state’s general budget is lost,” a government source told Reuters, adding that announcing the election swiftly should overshadow the budget vote defeat and create a more positive news flow, helping the Socialists.

A senior Socialist party source confirmed that the announcement of a snap election would probably come quickly: “It is likely, as soon as the voting (on the budget) ends.”

Tensions were high again between Madrid and Barcelona as the first day of budget debates coincided with the start of a trial of 12 Catalan separatist leaders in Madrid over their role in the region’s failed independence bid in 2017.

“If there is no budget, it won’t be the Catalan pro-independence parties’ fault, it will be because you think you will benefit from an early election,” said Ferran Bel, from the Catalan PDeCat party, addressing the government.

Catalonia’s regional government head Quim Torra, in Madrid for the opening of the trial, which he called “an attack on democracy and human rights”, told reporters self-determination via a referendum had to be part of any dialogue with Madrid.

“We are not demanding anything that isn’t democratic, that wouldn’t be done via ballot boxes,” he said. “One cannot govern against Catalonia, against the will of its people.”

In an early morning tweet, Sanchez had said he expected both right-wing and pro-independence lawmakers to vote against his budget. “They both want the same: A divided Catalonia and a divided Spain,” he said.

The sources did not say when Sanchez would announce the snap election.

His Socialists hold less than a quarter of the seats in the lower house, and speculation about whether it will serve a full term has been rife since it took office last year when the conservative People’s Party lost a confidence vote.