Catalan political chief Artur Mas's ruling coalition and a majority of other parties in the northeastern Spanish region are calling for a November 9, 2014 referendum that would ask voters two questions:
"Do you think that Catalonia should be a State, yes or no?"
"If yes, do you want that State to be independent, yes or no?"
Many Catalans point to Scotland, whose leaders have called a referendum for September on independence from Britain - a move authorised by the British government.
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The proposal appears doomed from the start, however, given that a Catalan independence referendum is opposed by Spain's two largest national parties: the ruling conservative Popular Party and the main opposition Socialist Party.
Three members of the Catalan Socialist Party broke ranks with their national party in the latest vote, casting ballots in favour of the proposal. Another Catalan Socialist lawmaker gave up his seat on the eve of the vote so as to avoid having to cast a 'no' vote in line with his party's policy.
"It is unconstitutional and it will not take place," Rajoy told a news conference just hours after the plan was unveiled.
"This initiative collides head-on with the foundation of the constitution which is the indissoluble unity of the Spanish nation," the premier said.
Rajoy has argued that Catalonia cannot hold a referendum like Scotland because Spain, unlike Britain, has a written constitution that rules out such a move.
Proud of their distinct language and culture and fed up after five years of stop-start recession, many of the 7.5 million people in Catalonia want to redraw the map of Spain, saying they feel short-changed by the central government which redistributes their taxes.