Tensions continue to escalate between the Spanish central government and Catalonia's regional government. Madrid is increasing legal, economic and political pressure over Catalan authorities in an effort to disrupt the organization of an independence referendum on Oct. 1. On Sept. 20, Spanish police entered several Catalan government offices in Barcelona, seized documentation related to the referendum and arrested at least a dozen Catalan government officials. In response, thousands of pro-independence demonstrators took to the streets in Barcelona to protest. The actions of the Spanish police are part of Madrid's larger strategy to undermine Catalonia's independence vote , which the Spanish Constitutional Court has declared illegal. In recent days, police have entered several print shops and seized thousands of pro-referendum posters and pamphlets, as well as ballots. On Sept. 19, they seized boxes containing an estimated 45,000 envelopes with the Catalan government's logo in the city of Terrassa.