Barcelona, Spain - Catalan protesters in Barcelona are calling for the release of two men they consider the first "political prisoners" in their quest for independence.

Jordi Cuixart of Omnium Cultural and Jordi Sanchez of the National Catalan Assembly (ANC) were imprisoned without bail in Madrid on Monday, pending a trial on charges of sedition in relation to their separatist organising efforts.

"They are political prisoners," Jordi Graupera, a Catalan author and postdoctoral researcher at Princeton, told Al Jazeera. "They are being punished for being successful in their peaceful resistance strategy."

Omnium and the ANC are grassroots organisations that have long assisted in pro-independence campaigns, including the disputed October 1 referendum on Catalan independence.

On Monday night in Barcelona, people banged pots and pans outside their windows in protest. On Tuesday, a city-wide "stop" in work began at midday in a show of solidarity.

By Tuesday evening, a group of 50 people, comprised of two separate organising committees (CDRs), marched towards the Spanish delegation in Barcelona.

Their number seemed to grow with each block as they chanted "Freedom for Sanchez and Cuixart!"

Anna Martinez, one of the CDR organisers, said she never thought the Spanish government would take political prisoners.

"It's shocking. The situation has become very serious," Martinez told Al Jazeera.

Joan Folch lived in France for 24 years and moved back in September because of the political situation.

He said he was outraged by the imprisonment of the pro-Independence leaders.

"Everyday the Spanish government gives us more reasons to continue the struggle," Folch said.

The group of 50 met with a larger block of protesters at the beginning of Diagonal, one of Barcelona's main thoroughfares.

Though the demonstration is blocking the traffic, drivers honked in support.

Folch said the Catalan national movement is unique in that it has support from the political left to right.

By the time the CDRs and other groups reached the Spanish delegation, their numbers were in the thousands.

Demonstrators halted in front of the delegation and lit candles. Chants of "Freedom" rang out intermittently.

'Putting everyone in their place'

Spanish Justice Minister Rafael Catala said the Catalan leaders' imprisonment represented the "normal functioning of Spanish justice", adding, "we can talk about prison policy, but not political prisoners".

Xavier Garcia Albiol, leader of Catalonia's ruling right-wing Popular Party, applauded the decision to imprison Cuixart and Sanchez.

"Rule of law ends up putting everyone in their place," he tweeted.

But Josep Costa, a professor of political science at Barcelona's Universitat Pompeu Fabra, said the imprisonment marked "another episode showing the complete breakdown of rule of law in Spain".

"It's the government filing the charges and seeking the imprisonment of political opponents," Costa said.

Standoff

The imprisonment of Cuixart and Sanchez is the latest development in a heightening political crisis in Spain.

The Spanish constitutional court ruled the October 1 Catalan referendum unlawful, with Madrid ordering police to stop the poll while respecting voters.

But Spanish National Police and the Civil Guard, a military body tasked with law enforcement, used "excessive force" to stop the vote, according to rights groups.

Catalans voted to secede from Spain, but turnout was reportedly lower than 50 percent.

On October 10, Carles Puigdemont, Catalan president, declared an independent Catalan state and then suspended the effects of the declaration. He says his intent was to foster dialogue with Madrid.

Spanish Prime Minister Mariano Rajoy then gave him until Monday morning to clarify whether or not independence was declared., warning that he would enact Article 155.

Referred to as the "nuclear option", Article 155 of the Spanish constitution has never been used before and allows the central government to take control of Catalonia's regional government.

Puigdemont responded Monday with an offer of two months of dialogue, but failed to clarify the stance on independence.

Madrid has extended the ultimatum until Thursday morning. The central government has reiterated its warning that if Puigdemont does not clarify his stance by this deadline, Article 155 will be enacted.