The French government has said it will not recognise Catalonia if it declares independence from Spain and such a move will mean expulsion from the EU.
European Affairs Minister Nathalie Loiseau said the crisis following the banned 1 October referendum had to be resolved through dialogue within Spain.
Catalan President Carles Puigdemont is expected to address the regional parliament on Tuesday.
There has been no sign of a compromise being struck with Madrid.
Economic pressure on the pro-independence camp is rising with three more companies expected to discuss moving their offices out of Catalonia on Monday, sources told Reuters news agency.
These are infrastructure firm Abertis, telecoms company Cellnex and property group Inmobiliaria Colonial.
Major lenders Caixabank and Sabadell announced earlier that they were moving their offices out of the region.
The region of Catalonia, home to 7.5 million people in the north-east, is crucial to Spain, which is the EU's fifth-biggest economy and a member of Nato.
In other developments:
Catalonia's High Court asked for Spanish national police to provide extra security at the court building in the event of the Catalan parliament declaring independence; the building is currently guarded by local police
The leader of Spain's Socialist opposition party, Pedro Sanchez, told reporters in Barcelona that his party would back government action if independence was declared unilaterally on Tuesday: "We reach out for dialogue but we'll support the response of the rule of law in the face of any attempt to break social harmony"