Spain's prime minister is urging the people of Catalonia to refrain from taking part in a planned referendum on the region's independence that he says is unconstitutional.
If the "Yes" side wins, Catalonia's regional government has vowed to declare independence within 48 hours and set about building a sovereign state.
Over 700 municipal leaders pledged to help facilitate the vote, although the mayor of Barcelona has not yet taken a definitive position.
Following a legal challenge from his government, Spain's Constitutional Court suspended a referendum law that was fast-tracked through Catalonia's regional parliament on Wednesday.
The country's prosecutor office on Wednesday ordered the 712 mayors, who have agreed to help stage the October 1 vote, to be summoned to court as official suspects and called for their arrest in case of a refusal to appear for questioning.
"They can't arrest us, they're insane!", David Rovira, the pro-separatist mayor of L'Espluga de Francoli, a town of some 3,800 residents, told AFP news agency, adding that Madrid had "proposed nothing" to appease Catalonia's demands for greater autonomy.
Police were ordered on Tuesday to seize ballot boxes, along with election flyers or any item that could be used in the banned referendum, AFP reported.
Prime Minister Mariano Rajoy, whose conservative government is fiercely against the vote, wished Catalonia "a good day", calling "for a Diada of freedom, cohabitation and respect for all Catalans". The following day, the Constitutional Court of Spain suspended the new law.
Rajoy said on Wednesday: "If anyone urges you to go to a polling station, don't go, because the referendum can't take place, it would be an absolutely illegal act".
As tensions over the independence referendum reach record heights, Spain's King Felipe VI made his first public statement since Catalonia's government passed a bill in their parliament that details the referendum and established an "exception judicial regime" in the wealthy north-eastern region of Spain.
On Monday, hundreds of thousands of Catalans marked their national holiday by supporting the right to vote and become independent.
Catalonia, which is roughly the size of Belgium and accounts for about one-fifth of Spain's economic output, and already has significant powers over matters such as education and healthcare.