Catalans have said during 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 in Barcelona on Sept. 11 for the largest nationalist rally in the region since the 1970s.
These growing economic concerns have combined with a longstanding nationalist streak in Catalonia, which has its own 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.
One of the most potent symbols of the divisions distancing Catalonia and the country's capital city can be seen in the bitter rivalry between the Barcelona and Real Madrid soccer clubs.
In recent years grassroots groups have held unofficial referendums on independence in towns throughout the region, while some small villages have gone to the extreme of declaring themselves "free Catalan territories."
Catalans are viewed by most Spaniards as thrifty, hardworking people, and most -- not least many Catalans -- have been shocked by how their regional debt has swelled to 42 billion euros ($54.4 billion) of the staggering 140 billion euro debt ascribed to all of Spain's regional governments.
The economic crisis has highlighted the high cost of running Spain's 17 semi-autonomous regions alongside a central government. The Catalan government has had to ask for a 5 billion euro ($6.5 million) bailout from Spain like other indebted regions.
Mas' government counters that each year it contributes 16 billion euros ($21 billion) more than it gets back from Spain. It also complains that important infrastructure projects needed to revive Spain's sick economy are being left unfunded.
Even so, many people feel they are both Catalan and Spanish, and are wary of the idea of trying to divide the country.