Prime minister Mariano Rajoy has taken action through the courts to rule the referendum illegal and promised to use the Civil Guard to attempt to seize the ballot boxes as well as raid the offices of a printers in Tarragona who were believed to be printing ballot papers. The Spanish king Felipe VI said on Wednesday (13 September) that the Constitution would prevail in case of any breach, and that the rights of all Spaniards would be preserved.
Anti-secession sentiment is being supported at the EU level as well, with European Union officials warning that even if Catalonia did successfully secede, it wouldn't mean they'd become members of the European Union.
Both the Catalans and the Kurds considers themselves a separate nation.
Polls show a minority of Catalans want self-rule, although a majority want the chance to vote on the issue.
Catalonia will stop sending weekly financial accounts to Madrid, defying a demand by Spain's central government that the region prove it is not using public money to promote an independence drive.
A concern for those holding the referendum is the possibility of a low turnout by No voters who are deterred by the referendum's illegal status.More news: Jason Stockley found not guilty of murder by judge's ruling
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If they win, the separatists vow to declare independence within days for the wealthy northeastern region of Spain, with its capital Barcelona, home to around 7.5 million people. That might lead to a distorted result that heavily favours independence but which fails to represent all Catalans.
Ramon Pique, the coordinator of the Catalan National Assembly campaign, has said however that the determination of the state to prevent the independence referendum from being carried out might actually have the effect of boosting support among Catalan's for independence.
Catalan president Carles Puigdemont arrives to an event marking the start of campaigning for the independence ballot in Tarragona on Thursday night.
A spokesman for the Catalan regional government declined to say where the ballot boxes were or how the government was going to get them out of hiding to voting stations on October 1.
Mr Puigdemont and other Catalan leaders including Barcelona Mayor Ada Colau appealed in an open letter on Friday for an eleventh-hour dialogue with the Spanish government, complaining of "unprecedented repression".
Colau and her Barcelona en Comú platform had been ambivalent about the referendum, a stance that has been taken by much of Spain's so-called New Left, which is spearheaded by Podemos.