The Spanish government has warned Catalonia's separatist leader not to do anything 'irreversible'.
This was just hours before a possible declaration of independence that could send shockwaves through Europe.
Whether or not Catalan president Carles Puigdemont will follow through on his threat to announce a full breakaway - defying the central government and Spanish courts - is still a mystery.
The Spanish government issued a warning to Puigdemont as it grapples with the nation's worst political crisis in a generation.
"We call on Puigdemont not to do anything irreversible, not to pursue a path of no return and not to make any unilateral independence declaration," government spokesman Inigo Mendez de Vigo told reporters.
Speaking soon afterwards, Catalan government spokesman Jordi Turull retorted that the regional executive was 'completely united', without giving any hint of what Puigdemont may tell Catalan lawmakers in an extraordinary parliamentary session beginning at 1600 GMT.
At stake is the future of a region of 7.5 million people deeply divided over independence, one of Spain's economic powerhouses whose drive to break away has raised concern for stability in the European Union.
Political leaders in Catalonia, Spain, and Europe have urged Puigdemont to stand down and ease the country's biggest upheaval since its transition to democracy in the 1970s.
But the Catalan president says an independence referendum that took place on October 1 despite a court ban ruling it unconstitutional justifies splitting from Madrid.
Around 90 per cent of those who cast ballots voted for independence but the poll was poorly monitored and many Catalans opposed to secession simply stayed at home. Turnout was just over 42 per cent.
Spain's Economy minister Luis de Guindos on Tuesday denounced the independence call as a 'rebellion against the rule of law'.
Catalan police were out in full force around the region's parliament in Barcelona ahead of Puidgemont's address.
"The end of the road," said Catalan daily El Periodico on its front page.
On Monday, Ada Colau, the popular mayor of Barcelona, warned that a unilateral declaration of independence would put 'social cohesion' at risk.