Spanish PM Mariano Rajoy says he will ask the courts to revoke a law passed by the Catalan regional government to hold a referendum on independence, the BBC reports.
He described the vote, planned for 1 October, as illegal.
Earlier, state prosecutors said they would bring criminal charges against Catalan leaders for their endorsement of the referendum.
The pro-independence majority in Catalonia’s parliament passed the referendum law on Wednesday.
Spain’s wealthy north-eastern region already has autonomous powers but the regional government says it has popular support for full secession.
“What is not legal, is not democratic,” said Mr Rajoy.
He described the law as an “intolerable act of disobedience” and said the constitutional court would be asked to nullify it.