On Sunday, the representatives of the far-left party of Ada Colau, the mayor of Barcelona, voted to break up their governing coalition in Barcelona’s City Hall with the Socialists, because the Socialists had backed Mr. Rajoy’s decision to take over Catalonia’s administration.
In response, Miquel Iceta, the Socialist leader in Catalonia, accused Ms. Colau’s party of choosing Catalan independence over the interests of Barcelona.
On Twitter, Ms. Colau called the breakup of her governing coalition on Sunday “a difficult decision.” She recently had criticized the separatist lawmakers for unilaterally declaring independence. Still, the mayor joined the protest on Saturday to demand the release of eight jailed former members of the Catalan government, as well as that of two other separatist leaders.
About 750,000 people marched in Barcelona, according to the local police. From Brussels, Mr. Puidgemont thanked the demonstrators, on Twitter, for being “our strength.”
On Sunday, however, Mr. Rajoy called on “the silent or silenced majority” that opposes secessionism to “convert its voice into votes” on Dec. 21. In the most recent regional elections, in September 2015, separatist parties won a majority of the seats in the Catalan Parliament, but with only 48 percent of the votes.
The leading candidate of the Popular Party in Catalonia, Xavier García Albiol, told supporters that “independence is toxic and destroys Catalonia.”
Mr. García Albiol condemned suggestions that Catalan separatist leaders were being held in Madrid jails as political prisoners.
“Spain is today is one of the most consolidated democracy of Europe and the world,” he said.
Both Mr. Rajoy and Mr. García Albiol highlighted the negative financial consequences of the secessionist conflict and assured Catalan voters that they would help return the region to economic health by beating the separatist parties next month.
Mr. Rajoy urged Spanish consumers not to boycott Catalan goods and said that he was determined to stop separatists from pursuing “a journey to nowhere, that will again bring crisis, unemployment and the fracture of Catalan society.”
Mr. García Albiol said that more than 2,400 companies had moved their legal headquarters from Catalonia since the start of October.
“Never have companies left any part of the world so quickly,” he said.