Catalonia's regional government insists a vote will take place on October 1 but the Spanish government has vowed to block it, describing it as "unconstitutional".
More than two-thirds of the autonomous region's mayors have said they will facilitate the vote and allow municipal buildings to be used, in violation of Madrid's orders.
More than 700 mayors gathered in Barcelona Saturday to march through the streets of Catalonia's cosmopolitan capital. On Friday, Catalonia's highest court also issued a warning to seven local newspapers not to print any notices for the independence referendum.
Organisers said 35,000 people rallied in the northern city of Bilbao - a symbolic protest in a region still marked by decades of violence once waged by armed separatist group ETA, and where the desire for independence remains strong.
Polls in July showed that 70 percent of Catalans want the chance to vote on their independence.
She pointed to the Edinburgh Agreement, signed in the build-up to the Scottish independence referendum, as to how governments can work together in such circumstances.
Catalonia's regional police force is under orders to arrest the mayors if they refuse to appear for questioning in an investigation into the vote, which Spain's constitutional court has suspended, State Prosecutor Jose Manuel Maza's office said.
Spanish police on Saturday seized printing materials meant to support and promote the referendum near Barcelona.
Spanish Prime Minister Mariano Rajoy is bringing the full weight of the state to bear to prevent Catalonia's independence referendum. Taxes, foreign affairs, defence and infrastructures are in the hands of Spain's central authorities. Budget Minister Cristobal Montoro said on Friday that the central government would take over the funding of most essential public services in the region unless Puigdemont guaranteed public cash was not being used to fund the referendum.