Catalonia’s leader Carles Puigdemont is facing a final deadline to drop a secession bid, with Spain warning it will suspend the region’s autonomy if he fails to do so by 10:00 (08:00 GMT).
After a referendum on 1 October, he signed an independence declaration but then suspended it, asking for dialogue.
Reports suggest he will press ahead on independence if Madrid moves to take direct control.
There are fears that this may lead to civil unrest in Catalonia.
Article 155 of Spain’s 1978 constitution, which cemented democratic rule after the death of dictator General Franco three years earlier, allows Madrid to impose direct rule in a crisis but it has never been invoked.
In the lead-up to the deadline, there have been mass protests over the detentionof two leaders of the separatist movement.