A dispute between Spanish authorities and Catalan separatists over a yellow ribbon symbol is building into a hot issue ahead of Spain's general election next month.

The independence-minded Catalan government has failed to obey an order from the country's electoral board to remove from the region's public buildings the large ribbons, which are a protest at the imprisonment and trial of separatist leaders for their role in a failed attempt to declare independence in 2017.

Quim Torra, Catalonia's regional president who always wears a small yellow ribbon in his lapel, has asked the board for more time to remove the symbols after a deadline passed.

Pablo Casado, the leader of Spain's main opposition Popular Party, on Wednesday called on Prime Minister Pedro Sanchez to take a tougher stance against Catalan separatists.