Thousands of workers in Barcelona and other cities staged a brief walkout at noon in protest over Monday's move by the National Court in Madrid to keep Jordi Cuixart and Jordi Sanchez behind bars on sedition charges.
"Repression is not the solution," protesters shouted as hundreds gathered outside the Catalan regional government offices in central Barcelona.
"Now anyone can be put in jail," said Carme Guell, a 62-year-old beautician who joined the walkout as civil servants from nearby regional ministries blocked the street.
Like many who back independence for semi-autonomous Catalonia -- which is profoundly divided on the issue -- Guell said the wealthy northeastern region was "treated like a colony. All our money is taken away, nothing is reinvested here".
Catalonia's separatist government sparked Spain's worst political crisis in decades by holding a banned independence referendum on October 1, when a violent crackdown on voters by national police shocked the world.
As the standoff shows little sign of easing, Madrid announced late Monday that it was cutting its growth forecast for next year from 2.6 to 2.3 percent.
The prolonged uncertainty has rattled the stock markets, while nearly 700 companies have moved their legal headquarters out of Catalonia, according to official figures released Tuesday.
Further protests against the detention of Cuixart and Sanchez were planned for Tuesday afternoon in front of central government offices in Barcelona, Girona, Tarragona and Lleida, with a candle-lit protest in Barcelona at 8:00 pm.
The pair nicknamed the "two Jordis" are the leaders of pro-independence citizens' groups Omnium Cultural and the Catalan National Assembly (ANC) respectively, both of which count tens of thousands of members and have emerged as influential players in the crisis.
They are accused of encouraging a major protest last month as Spanish police raided the Catalan administration's offices in the run-up to the referendum.
Police officers were trapped for hours and their vehicles vandalised as protesters ringed the building, with Cuixart and Sanchez standing atop a police car calling for "permanent mobilisation" against the Spanish state.
The crime of sedition can carry up to 15 years in prison.
"If you're watching this video, it's because the state has decided to deny me my freedom," Cuixart said in a message recorded before the court decision, adding that his organisation would work "underground" if necessary.
Though she opposes the current drive for independence, Barcelona Mayor Ada Colau blasted the move to detain Sanchez and Cuixart, who she said were being held as "political prisoners".
"The existence of political prisoners has no place in the current EU," she said, announcing the city council would halt meetings for two days in protest.
Catalan police chief Josep Lluis Trapero has also been charged with sedition for allegedly failing to stop the referendum. He has been allowed to walk free, but is banned from leaving Spain.
Enric Millo, the Spanish government's representative in Barcelona, insisted that the judge's decision had been made independently.
"There is a separation of powers here," he told Catalunya Radio.
Barcelona mayor Ada Colau (right) and Catalan regional president Carles Puigdemont in a protest outside the Generalitat. Photo: Lluis Gene/AFP
Madrid has given Catalan leader Carles Puigdemont until Thursday to clarify whether he is declaring independence following the referendum, which resulted in a 90 percent 'Yes' vote -- although turnout was only 43 percent as many supporters of Spanish unity stayed away.
Puigdemont stopped short of giving the definitive response that Madrid demanded on Monday and instead repeated his call for talks with Prime Minister Mariano Rajoy.
But anything less than a full climb-down is likely to prompt the central government to start imposing unprecedented direct control over the semi-autonomous region -- the so-called "nuclear option".
With its own language and culture, Catalonia is proud of its autonomy but its 7.5 million people are deeply split over whether to break definitively from the rest of Spain.
Supporters of independence say the region pays more into Spanish coffers than it gets back and could prosper by going it alone, but their opponents say secession would spell political and economic disaster.
Ratings agency Standard and Poor's has warned of a recession in Catalonia -- which makes up about a fifth of Spain's economic output -- if the crisis drags on.