They are cracking down on organisers by threatening them with prosecution.
For this reason some are now sitting up and looking out for the next potential flare-point - Spain's Catalonia region where seperatists are pushing for independence.
The chief prosecutor in Catalonia ordered police to seal off buildings that will house polling stations before the day of the referendum and deploy officers on the day of the vote to prevent ballots from being ast.
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.
"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.
President Trump said Tuesday that the United States opposes an independence drive in the Spanish region of Catalonia, telling reporters that such secession would be "foolish".
Sala is one of more than 700 mayors who have pledged to cooperate with the referendum.
Catalonia's separatist government, however, remains committed to holding it on Sunday.
And police have seized close to ten million ballot papers, as well as other items destined for the vote.
The Spanish prosecutor has previously warned that Catalan officials involved in the preparation of the referendum on independence could be charged with disobedience, abuse of power and embezzlement of public funds.
Faced with these actions, the separatist leaders of this wealthy northeastern region of Spain, home to around 7.5 million people, have accused Madrid of "repression".
But the unrelenting opposition from Madrid means such a result would go all but unrecognised, potentially setting up a new phase of the dispute.
Polls show that Catalans are sharply divided over whether they want independence, but a large majority would like a legal referendum to settle the matter.
He said: "I really think the people of Catalonia would stay with Spain".
The Catalan regional government, which plans to declare independence within 48 hours of a "yes" victory, maintained on Tuesday the vote will go ahead and it sent out notifications to Catalans to man polling booths across the region.
"They are excluding half the population", Dastis said.