The Spanish government has said it will block the ballot planned by Artur Mas by appealing to the Constitutional Court, AFP reported.
The decree, signed on Saturday, comes as the long-standing pro-independence movement in the north-eastern region continues to gather momentum in the face of recent years of economic hardship.
Spain's Prime Minister Mariano Rajoy has called an special cabinet meeting on Monday to formalise his government's legal challenge to the vote in the constitutional court.
The announcement comes a week after Scotland voted against breaking away from Britain in a referendum that some in Catalonia say inspired them to seek a similar poll.