Spain's Constitutional Court suspended the referendum law to allow judges time to consider whether the Catalan vote for an independence reference breaches the country's constitution.
Spain's central authorities moved on Thursday to crush plans by the northeastern region of Catalonia to hold an independence referendum and took steps to prosecute regional lawmakers backing the ballot.
A long-running campaign for independence by a group of Catalan politicians, who hold a majority in the regional parliament, came to a head on Wednesday when they approved a law to allow a vote on secession from Spain scheduled for October 1, sparking the country's deepest political crisis in 40 years.
The country's Constitutional Court, Spain's highest legal authority on such matters, suspended the referendum law late on Thursday to allow judges time to consider whether the vote breaches the country's constitution.
Prime Minister Mariano Rajoy said earlier on Thursday he had appealed to the court to declare the referendum illegal. The constitution states Spain is indivisible.
"This referendum will not go ahead," he said.
Catalan leaders to be charged
He also said all 947 mayors in Catalonia would be warned over their "obligation to impede or paralyse" efforts to carry out the vote which he said is unconstitutional.
The Catalan parliament will also meet again later on Thursday to examine a "transition law" laying out how the region would function if the majority of its 7.5 million inhabitants vote in favour of seceding from Spain.
Spain's top prosecutor meanwhile said "criminal charges are being prepared" against the leaders of the Catalan parliament as well as officials in the regional government who prepared the referendum decree and that voting materials would be seized.
General prosecutor Jose Manuel Maza told reporters the officials could be charged, among other things, with disobedience, abuse of power and embezzlement.
Maza added that regional prosecutors, assisted by police, had been told to investigate any actions taken to organise the vote.
"Covert state of siege"
The warnings were brushed aside by a Catalan government spokesman, who insisted the referendum would take place despite a "covert state of siege" being imposed by the central government in Madrid.
"Whether it's snowy or windy, we will do it because we have a contract with the citizens of Catalonia," Jordi Turull said.
"This does nothing to alter the government's project," he added. "Faced with this covert state of siege, we now feel obliged to defend our most fundamental rights."
Catalonia's president Carles Puigdemont, a lifelong proponent on independence, is hoping to mobilise supporters in a show of legitimacy in the face of Madrid's threats to halt the vote by any means possible.
He sent a letter to Catalonia's mayors on Thursday asking them to give notice within 48 hours of what locations they could make available for ballot stations.