BARCELONA, Spain — Catalonia’s regional government on Friday chose Oct. 1 as the date for a referendum on a split from Spain, stepping up the confrontation with the country’s central government, which sees the vote as illegal.

Regional president Carles Puigdemont said Catalans will be asked to answer yes or no to a single question: “Do you want Catalonia to become an independent state in the form of a republic?”

The country’s Constitutional Court has already invalidated previous attempts by the northeastern region to gain more autonomy. Several Catalan politicians, including former regional president Artur Mas, have been fined or barred from public office for holding a mock referendum in November 2014.

Prime Minister Mariano Rajoy’s conservative government called the announcement a “show” by those willing to divide Spain and swore to stop the vote if Catalan politicians or the regional parliament make a formal move toward holding the vote.

“There is not going to be any illegal referendum that goes against the Constitution,” the government’s spokesman, Inigo Mendez de Vigo, said after a weekly cabinet meeting. “We are facing an increasingly radical strategy that has less and less support.”

Earlier this week, Deputy Premier Soraya Saenz de Santamaria, who has been tasked by Rajoy to deal with Catalonia, said: “They can announce that referendum as many times as they want and delay it for weeks or hold as many events as they want, but the referendum will not be held.”

Puigdemont said the decision to call for the vote was reached after more than 18 months of efforts failed to establish a dialogue with Madrid.

He also said the vote was nonnegotiable because Catalans backed his plan for secession by voting for his coalition of pro-independence parties at the end of 2015.

“It is time for Catalans to decide their future,” Puigdemont said. “It is in our hands to prove that democracy unites us all above the legitimate and healthy discrepancies that characterize mature societies.”

Catalonia represents a fifth of Spain’s GDP and has a population of over seven million.

Separatists, who gained support as the economic crisis swelled the number of jobless, often say that the region’s future is brighter outside of Spain. They also say that an independent Catalonia would better defend their strong cultural identity and Catalan language.

Rajoy has opposed those arguments and recently said that the region could lose up to 30 percent of its GDP and that it would have to seek readmission to the European Union.

Polls consistently show that a large majority of Catalans are in favor of voting to change the current relationship between Catalonia and Spain, although the latest survey by the regional government exposed a declining support for independence, with 48.5 percent against and 44.3 percent in favor.

Members of the business community and some key political allies have distanced themselves from the unilateral referendum.

Barcelona mayor Ada Colau, a prominent figure in Spain’s new anti-establishment left movement, has rejected supporting a vote that is not agreed with central authorities.

Circulo de Economia, a civic association that includes a high number of prominent companies, urged both sides last month to resolve the conflict by finding “alternative means that are not just black and white.”

Its executive director, Jordi Alberich, recently told The Associated Press: “If we enter a dynamic of radicalization and going against the law, that’s a scenario that could certainly have dire consequences.”

Former Barcelona football team coach Pep Guardiola is expected to speak on Sunday at a march in the regional capital in support for the October vote.

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Parra reported from Madrid.