Nationalist leaders of the wealthy northeastern region have vowed to declare Catalonia independent within a year and a half if they win a majority of seats in the regional assembly in Sunday's polls.
Pro-independence leaders insist that should Catalonia secede, Catalans would be able to hold double Spanish-Catalan nationality as the constitution guarantees that no Spanish natives can have their nationality withdrawn.
"When we leave a country, it is evident that we abandon it with all the attributes that mean we are from this country," Garcia-Margallo told reporters in Barcelona.
The reality however is more nuanced.
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An agreement struck between France and Algeria allowed for Algerians born before 1963, independence year, to keep their French nationality.
For residents of Cuba, a former colony of Spain which gained independence in 1898, there were also special provisions for those born in Spain.
Garcia-Margallo's comments came a day after Spanish Prime Minister Mariano Rajoy warned that an independent Catalonia would mean a loss of EU membership, and that any attempt to break away "would have no legal value".