Families in favor of Catalonia’s independence from Madrid on Saturday took over thousands of polling stations to stop the central government from shutting down a referendum planned for Sunday. Spanish authorities said pro-independence demonstrators were occupying about 163 schools as of Saturday afternoon, vowing to camp out in the buildings that serve as polling stations. Police have issued an ultimatum to the demonstrators, demanding that they vacate the premises by 6 a.m. Sunday, three hours before the planned vote. It was not immediately clear what action would be taken if the voters refuse to leave, but Enric Millo, a high-ranking official in the region, said anyone who sticks around will be removed in line with a court order. “I trust in the common sense of Catalans and that people will operate with prudence,” he told the Associated Press. The independence vote has been declared illegal by the national government, and Spain’s Constitutional Court suspended it several weeks ago. But Catalonia’s government has called on millions of registered voters in the region to make sure the referendum goes ahead anyway.