The regional president of Catalonia was on trial Monday for allegedly disobeying Spain's electoral board by not removing secessionist symbols from public buildings in the northeastern region during an election campaign.
Quim Torra could be declared unfit to hold public office for a period of time if found guilty in the trial.
The secessionist movement in the wealthy region of 7.5 million is Spain's gravest political challenge in decades.
Polls show residents in Catalonia are roughly evenly divided over the question of independence from Spain, but the topic has ignited Spanish nationalism and fuelled the rise of the far-right Vox party.
Prosecutors are charging Torra with failing to comply with orders from the country's electoral board to remove yellow secession ribbon symbols from the regional government's headquarters in Barcelona before Spain's April 28 national election.
The ribbons are how Catalan separatists show support for the movement's leaders, nine of whom have received prison sentences this fall for their role in a failed secession bid in 2017.
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The board said the ribbons were "tools of political propaganda" that violated campaign laws.
Several hundred supports and fellow politicians accompanied Torra as he arrived at the court in Barcelona, the Catalan regional capital.
Torra, who is fervently in favour of Catalonia's independence from Spain and its right to self-determination, told the court he did not believe that the electoral board had the right to order him to remove the symbols.
If he is convicted and declared unfit to hold public office, Catalonia would likely have to call a new regional election.
Torra refused to answer prosecutors' questions and only replied to questions by his defense lawyers.
Spain's constitution rules that the country is indivisible.