The Guardia Civil searched several regional government headquarters in Barcelona, a Catalan government spokesman said.
The operation comes a day after police seized a trove of documents related to the independence referendum from the offices of private delivery company Unipost in the Catalan city of Terrasa.
Pro-separatist parties captured 47.6 percent of the vote in a September 2015 regional election in Catalonia billed as a proxy vote on independence, giving them a narrow majority of 72 seats in the 135-seat Catalan parliament.
But polls show Catalonia's roughly 7.5 million residents are divided on independence.
A survey commissioned by the regional government in July showed 49.4 percent of Catalans were against independence while 41.1 percent were in favour.
Over 70 percent of Catalans want a legal referendum on independence to settle the issue.
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