Barcelona's new leftist mayor Ada Colau removed a bust of the old King from city hall on Thursday afternoon, describing it as an "anomaly" given his June 2014 abdication.
Several other symbols of the monarchy could also be removed from public spaces in Barcelona, a city with "a long republican tradition," Colau's deputy Gerardo Pisarello told reporters.
The decision to remove the bust came just hours after King Felipe VI warned Catalan leaders to obey the law in their drive for autonomy, as tension mounted over the region's bid to break away from Spain.
The head of state added his voice to the warnings after Spain's conservative prime minister, Mariano Rajoy, sharpened his tone against Catalan nationalists.
"Public authorities are subject to the rule of law, and it is by respecting it that they guarantee the orderly functioning of the state," the king said.
"Respect for the law is the source of legitimacy and an unavoidable requirement for living together democratically in peace and freedom."
He did not refer to Catalonia or independence in his remarks, although they were made in an address in Barcelona that was attended by Catalonia's pro-independence regional president, Artur Mas.
The two main parties in the rich northeastern region of Spain -- Mas' centre-right CDC party and the left-wing ERC -- have formed a pro-independence alliance ahead of regional elections in September.
Since his June 2014 accession the throne, a symbol of the unity of Spain and its diverse regions, Felipe has issued discreet calls for unity over Catalonia.