"We denounce the attempt by the state to intervene in the police forces of Catalonia", Joaquim Forn, the head of Catalonia's interior department and the civilian head of the Catalan police, said Saturday, reading a statement on regional television.
"I will keep hoping until the last minute that the Catalan government has a change of heart and calls off the referendum", Millo said at a briefing in Barcelona on September 26.
Spanish authorities say the October 1 ballot on whether the Catalan region should secede from Spain is illegal.
The Spanish government has sent thousands of police officers to Catalonia in the run-up to Sunday's planned referendum.
As tensions surrounding the vote builds, Prime Minister Mariano Rajoy has canceled his trip to the Estonian capital of Tallinn for a European Union summit on Friday, Spanish media reported.
Spanish authorities want the names of officials running polling stations at schools and civic buildings, with a view to prosecuting them.
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Anyone in possession of the keys or entrance codes to a polling booth could be considered a collaborator to crimes of disobedience, malfeasance and misappropriation of funds, the order said.
Catalan President Carles Puigdemont has tweeted several links to websites directing people where to vote on Sunday, but these have been taken down after a court-ordered sites that facilitate such information be blocked.
The central government has described the move as illegal.
This has sparked protests in Barcelona and other cities. Should the vote take place, a "yes" vote is likely, given that most of the 40 percent of Catalans who polls show support independence are expected to cast ballots while most of those against it are not.
But the unrelenting opposition from Madrid means such a result would go all but unrecognized, potentially setting up a new phase of the dispute.
The independence movement is widespread enough that it is unlikely to dissipate if the regional government fails to convert a "yes" vote into a split from Spain. But a large majority of people are in favor of being given the right to vote on the matter, making Spain's heavy-handed approach all the more politically risky. He has promised to declare independence within 48 hours of a victory for the yes campaign.