The wealthy northeastern region launched its official campaign for an independence referendum on Thursday in defiance of Madrid, which has declared the process illegal, and the Constitutional Court, which has suspended the vote.
In a boost for the credibility of the referendum, the mayor of Barcelona said earlier on Thursday that the vote would go ahead in the city, having previously expressed concern that civil servants involved may lose their jobs.
"Due to the situation of manifest illegality in Catalonia, [the government] has established a mechanism of payment to guarantee public services to the Catalans", Montoro said at a press conference.
"Does anyone think we're not going to vote?"
Madrid was taking action because Catalonia's regional government has refused to comply with a request made back in July that it provide weekly instead of monthly accounts of its spending to ensure it was not using money to stage the contested referendum, Montoro said.
He said the arrangement implied "political control that is not related to the objectives of budget stability or to the purposes of state legislation in this matter". She also warned that facilitating the vote could be considered illegal.More news: European Union hardens measures against North Korea over weapons tests
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Sixteen days out from the planned referendum on October 1, Catalan President Carles Puigdemont and other top officials including the mayor of Barcelona released a letter appealing for an agreement on a vote and issuing "a new call to dialogue" without preconditions.
Police have been directed to arrest the mayors should they fail to answer the summons, according to the official letter sent to local authorities.
The European Commission president was asked for his thoughts on the referendum that Catalonia's leaders have pledged to hold on October 1 - and that Spanish Prime Minister Mariano Rajoy has vowed to stop at all costs - in an interview with young YouTubers.
"Right now, we have no idea where they are", he said. On November 9, 2014, about 80 percent of the Catalans who took part in a non-binding referendum on the region's status as part of Spain voted in favor of Catalonia becoming an independent state.
The letter accused the Spanish state of "an unprecedented repression offensive". They add that "between Catalonia and Spanish State re is an obvious political conflict that comes from far away and we tried to resolve with maximum agreement".
Most of Catalonia's 5.5 million voters want to have a say on the region's relationship with Spain, but the independence cause has lost support in recent years and surveys now indicate less than half the population would choose full self-rule.