The new procedure allowing the wealthy region to declare independence within 48 hours of the referendum's passage deepens the tension between Barcelona authorities and the central government in Madrid.
Catalan lawmakers approved the change on a 72-63 vote today.
The Spanish government has challenged in Spain's Constitutional Court nearly every step toward independence taken by the Catalan government and has succeeded in blocking most of them.
Prime Minister Mariano Rajoy's government made no immediate comment.