Spain's state prosecutor is seeking charges of rebellion, sedition and embezzlement against members of Catalonia's ousted secessionist government.
It pushes the crisis over the region's independence declaration into an uncertain new phase.
Jose Manuel Maza said he would ask judges for preventive measures against the politicians and the governing body of the Catalan parliament that allowed a vote to declare independence last week.
He did not specify if they would include their immediate arrest and detention before trial.
The charges carry maximum sentences of 30, 15 and six years in prison respectively.
Mr Maza did not name any of those facing charges, but they include regional leader Carles Puigdemont, his number two Oriol Junqueras and Catalan parliamentary speaker Carme Forcadell.
The announcement came as Catalonia's civil servants returned to work for the first time since Spain dismissed the separatist regional government and imposed direct control.
In addition to the sedition charges, Spain's government has said the fired leaders could be charged with usurping others' functions if they attempt to carry on working.
Mr Puigdemont travelled to Brussels, according to a Spanish government official, after Belgian asylum state secretary Theo Francken said over the weekend it would be "not unrealistic" for him to request asylum.
The ousted Catalan president's Belgium lawyer said it is not decided yet whether he will be seeking political asylum.
Paul Bekaert told VRT network that Mr Puigdemont "consulted me and came to ask for advice".
He added: "He is not in Belgium to specifically ask for political asylum. That is not decided yet."
The uncertainty over Mr Puigdemont's plans continue the game of political cat-and-mouse with which the Catalan leader has tormented the central government.
An official said the Catalan parliament has been formally dissolved and that its speaker will lead a transitional committee of legislators until a regional election is held on December 21.
A parliamentary spokeswoman said speaker Carme Forcadell has cancelled a Tuesday meeting of the regional parliament's speakers' body.
Prime minister Mariano Rajoy on Friday ordered the regional parliament's dissolution to try to find a way out of the political crisis.
Separatist legislators had passed a declaration of independence in the regional parliament on Friday.
Mr Puigdemont's party has indicated it is ready to fight in the December 21 regional elections called by the national government, scotching fears the pro-independence parties might boycott the ballot to deny it legitimacy.
The centre-right PDeCAT party vowed to defeat pro-union political forces in Catalonia.
As dozens of journalists, curious onlookers and bemused tourists gathered in the square outside the Gothic government palace in central Barcelona, a t least one portrait of Mr Puigdemont was still hanging on a wall inside the Generalitat building.
At least one member of the ousted government defied his dismissal by showing up at work and posting a photo on Twitter from his formal office.
"In the office, exercising the responsibilities entrusted to us by the people of Catalonia," said Josep Rull, who until last week was the region's top official in charge of territorial affairs.
Spanish authorities said deposed officials will be allowed to take their personal belongings from official buildings, but are barred from performing any official duties.
Catalonia's regional parliament proclaimed independence from Spain in a secret ballot on Friday.
The Spanish government dissolved the legislature, fired the government and regional police chief and called the new elections.