Hundreds of thousands of flag-waving demonstrators, calling themselves a "silent majority", packed central Barcelona on Sunday to protest against the plan, which has sparked the country's worst political crisis in a generation.
"Catalonia belongs to us all, and not just to the nationalists", said Álex Ramos, of the anti-separatist Catalan Civil Society, which organised the protest.
Republican Catalan Left (Esquerra, ERC) MP Joan Tardà tweeted: "Yes, Pablo Casado, we know how our President Companys ended up, shot by the army. This would likely trigger a decisive reaction by Spanish courts and the government of Prime Minister Mariano Rajoy", said Piccoli.
If it became independent, Catalonia would automatically be excluded from the european Union, it could join only after a new accession process.
Tempers have worsened over the past week after national police cracked down on voters during a banned October 1 Catalan independence referendum.More news: India Defense minister teaches Chinese soldiers meaning of 'Namaste'
Salellas says that Tuesday's parliamentary session in Barcelona will be an "act of sovereignty" in which "a political subject called Catalonia decides to self-determine and declare itself a republic". After declaring independence for the region in 1934, Companys was sentenced to 30 years in prison for rebellion.
A top Catalan official says the regional government is willing to talk to the central government, blaming Madrid for the impasse, even as other officials in Barcelona hint at pursuing a more drawn out declaration of independence, lasting perhaps weeks or months.
In an interview with the French TV station CNews, Nathalie Loiseau, France's minister of European affairs, said any declaration of independence would leave Catalonia isolated.
Speaking to Catalonia's TV3 on Sunday night, Puigdemont said he was unhappy with the Spanish government's unwillingness to negotiate over the issue, adding: "If the Spanish state doesn't respond positively, we'll be forced do what we came to do". Madrid has expressed concerns that the regional parliament may vote for a unilateral independence from Spain.
Catalonia, a northeastern region about the size of Belgium, is home to 7.5 million people and accounts for a fifth of Spain's economy.
So far, European Union officials have condemned the use of violence, but refused to be drawn into the conflict, which they see as an internal matter for Spain. Since last week, the region's two largest banks and some of its biggest companies have relocated to elsewhere in Spain.