Catalan president Artur Mas has called for the autonomous region to hold its own vote on independence from Spain on November 9th.
Spanish Prime Minister Rajoy has vowed to use the constitutional court to block the Catalan vote, but Mas said it is "impossible" to do so.
Marcelino Sexmero, spokesperson for the Francisco de Vitoria judge's association told media on Friday that disobeying the constitutional court would be "a new deed in the Spanish state" and as such it remained to be seen with which crimes the organizers of any illegal referendum would be charged with.
The first step, he said, would be to "create or uphold a resolution of holding an illegal referendum" which "could lead to serious disobedience of the national government".
According to Spanish daily El Mundo, Sexmero then added sedition to the list of possible charges, saying, "Of course there'd be misrepresentation, and disobedience would be the second, and sedition would depend on the attitude of the Catalan government".
Sexmero noted that any use of the Mossos de Esquadra, the Catalan regional police force, to assist the conduction of any referendum could be considered a crime of sedition which could carry a penalty of 15 years in prison.
The crime of serious disobedience of the government, which could be applied to organizers of any referendum, could lead to a six month to one year prison term, according to Sexmero.
Sexmero was speaking in the wake of massive public demonstrations in Barcelona on Thursday when as many as 1.8 million Catalans peacefully gathered to demand the right to vote on independence.
They gathered in the red and yellow colours of the Catalan flag to form a giant 'V' for 'Vote' along the city's two biggest streets.
"This V is a very powerful message and very wide-reaching, and those in Madrid should listen to it," said Mas after Thursday's rally.
"The time has come for them to sit down and negotiate."
Nationalists and political experts alike said this raised the question of how long the Spanish government could resist without flinching, and how Europe would tackle a potential wave of secession demands.
"The problem is no longer just with Catalonia," said Fernando Vallespin, a political scientist at the Autonomous University of Madrid.
"The question of how you solve it depends not only on Spain but on the European Union. People are very worried about it."
Spain's constitution, approved by referendum in 1978 three years after the death of the dictator Francisco Franco, gave the country's regions a degree of autonomy, but not as much as some Catalans now want.
"Nearly 40 years have now passed and that agreement needs to be revised," said Anton Losada, a political scientist at Santiago de Compostela University.
"There is a real demand in society for a change in the structure of the Spanish state."
Whatever happens on November 9th, something may budge in the standoff once that sensitive date is passed, Losada said.
The ruling Popular Party "has been gradually realising that something will have to be done with the constitution ... Now the question is how far-reaching to make that reform," he said.
"There is a real demand that requires a political response," he added.
"Either you change, or you adapt, or it explodes."