MADRID — Spain’s Supreme Court on Monday effectively barred Catalonia’s regional president from his office for refusing to remove a banner that called for the release of imprisoned separatist leaders and was displayed on a public building ahead of the 2019 general election.

The ruling that Quim Torra disobeyed Spain’s electoral law triggers a new period of political uncertainty in the northeastern region where a demand by some for independence has triggered the country’s biggest constitutional crisis in decades.

According to the existing regulations, Torra’s deputy should take over as president-in-charge until the regional parliament elects a new leader or a new election is held.

Pro-secession activists reacted by calling for protests in the regional capital, Barcelona.

In their ruling, the panel of judges unanimously agreed to uphold last year’s decision by a lower court to ban Torra from holding any public office for 18 months and fine him 30,000 euros ($35,000).

Torra, a staunch separatist who became the head of Catalonia’s government following the 2017 push for the region’s independence from Spain, had previously criticized the case as an act of repression against the democratic mandate of voters in the region.

His predecessor, Carles Puigdemont, who fled to Belgium after the Spanish government deposed him for pushing ahead with an independence declaration, criticized the court’s decision.

“Once more, the Spanish state interferes in our democratic institutions,” Puigdemont wrote in a tweet.

Torra had remained at the helm of Catalonia during the appeal but Monday’s decision must be implemented even if the case is taken to the European Court of Human Rights, as pledged by Torra’s defense team.

The banner at the center of the case referred to a dozen former Catalan Cabinet members, lawmakers and activists who were imprisoned or left Spain following a declaration of independence in October 2017.