Spain's prime minister has urged the Senate to grant special constitutional measures that would allow the central government to take control of Catalonia's autonomous powers to try to halt the region's independence bid.
Mariano Rajoy, who received rapturous applause before and after his impassioned speech, told the chamber Spain is facing a challenge not seen in its recent history.
He said what is happening in Catalonia is "a clear violation of the laws, of democracy, of the rights of all, and that has consequences".
Mr Rajoy said the government's first move would be to dismiss Catalan President Carles Puigdemont and his ministers if the Senate approves the Spanish government's use of Article 155 of the constitution in a vote later on Friday.
He said the special measures are the only way out of the crisis, and that Madrid is not trying to take away liberties from Catalans but instead protect them.
Catalonia's regional parliament is also expected to hold a special session. The Catalan government rejects the moves by Madrid and there is speculation the regional parliament may take the step of declaring independence later in the day.
It will be the first time in four decades of democratic rule that the national government would directly run the affairs of one of Spain's 17 semi-autonomous regions, a move that could fan the flames of the Catalan revolt.
Mr Rajoy says the measures are aimed at restoring order and has promised to call a new regional election once that is achieved.
Mr Puigdemont scrapped hopes of a possible end to the political deadlock on Thursday when he opted not to call an early election himself and halt the drift toward independence.
The parliamentary sessions in Madrid and Barcelona are likely to last several hours before each votes on their resolutions.
Mr Rajoy's conservative Popular Party has an absolute majority in the Senate, thus guaranteeing the approval of his proposals, but he has also sought support from the country's main opposition parties. It will then be up to the government when to implement them.
Catalonia represents a fifth of Spain's gross domestic product. Polls show its 7.5 million inhabitants are roughly evenly divided over independence.
Meanwhile, the spokesman for the leading opposition party in Catalonia ripped to pieces a copy of the proposal by separatists to declare independence for the region.
Carlos Carrizosa, of the pro-union Citizens party, tore up the copy of the proposed law during Friday's debate prior to the expected vote in Catalonia's parliament.
He said: "With this paper you leave those Catalans who don't follow you orphaned without a government, and that's why Citizens won't let you ruin Catalonia."
He added: "Today is a sad, dramatic day in Catalonia. Today is the day that you (secessionists) carry out your coup against the democracy in Spain."
Secessionists hold a slim majority in the parliament based on less than half the vote due to Spanish elections law which gives more representation to sparsely popular areas.