While Rajoy is immersed in combating Spain's worst financial crisis in decades, Mas claims Catalonia is being asked to shoulder too much of the tax burden and that it could do better if it separated and tried to become an independent member state of the European Union.
"Five years ago I was in favor of a federal model with Spain, but now we have seen that is not viable," said Miquel Angel Aragon, a 37-year-old aid worker. "I am in favor of independence."
Catalonia is responsible for around a fifth of Spain's economic output and many residents feel central government gives back too little in recognition of the region's contribution.
Catalans have said in growing public protests that their industrialized region is being hit harder than most by austerity measures aimed at avoiding a national bailout like those needed by Greece, Ireland, Portugal, and Cyprus.
Madrid has traditionally said that simplifying the state's financial model by excluding overall costs such as defense only creates a distorted image of how taxation and spending are distributed.
A rising tide of Catalan separatist sentiment was spurred when Rajoy failed to agree to Mas' proposals to lighten Catalonia's tax load and 1.5 million people turned out for the largest nationalist rally since the 1970s in Barcelona on September 11.
These growing economic concerns have combined with a long-standing nationalist streak in Catalonia, which has its own language and cultural traditions that were harshly repressed by the military dictatorship of Francisco Franco from the end of Spain's Civil War in 1939 to Franco's death in 1975.