The move raised the stakes in Spain's deepest political crisis in a generation.
Violence erupted last weekend during Catalonia's independence referendum outlawed by Madrid.
Catalan regional president Carles Puigdemont lashed out at the government's "catastrophic" handling of the crisis and said he was open to mediation.
But Prime Minister Mariano Rajoy's office retorted that the government "will not accept blackmail."
Rajoy himself today called on Catalan leaders to "return to legality," in an interview with the Spanish news agency EFE.
But the Constitutional Court today ordered the session to be suspended while it hears an appeal by rival politicians.
It warned that any session carried out in defiance of its ban would be "null."
It said the parliament's leaders could face criminal action if they ignore the court order.
Puigdemont and other Catalan leaders have said they are not afraid of going to jail over their independence bid.
They carried out the referendum in defiance of a ban by the Spanish court and stern warnings from the national government in Madrid.
The vote on Sunday saw shocking scenes of police with batons beating unarmed voters.
The vote was not carried out according to regular electoral standards but Puigdemont said it had lent legitimacy to the independence drive.
If Catalonia declares independence, Spain could respond by suspending the region's existing autonomous status and imposing direct rule from Madrid.
The speaker of the Catalan parliament Carme Forcadell warned such a move "would just increase support for the pro- independence side."
Catalan authorities claim 42 per cent of voters cast ballots in the referendum and that 90 per cent of those backed independence.
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