The Spanish electoral system is regulated under the General Electoral System Organic Law 5/1985. Voting is on the basis of universal suffrage, with all nationals over eighteen and in the full enjoyment of all political rights entitled to vote—the only exception being in 1977, when this was limited to nationals over twenty-one and in the full enjoyment of all political and civil rights—. A 2011 amendment to the electoral law required for Spaniards abroad to apply for voting before being permitted to vote, a system known as "requested" or expat vote (Spanish: Voto rogado). Provinces are entitled to an initial minimum of two seats, with additional seats awarded in proportion to population. The number of seats allocated to León is currently set at four. Deputies are elected using the D'Hondt method and a closed listproportional representation, with a threshold of 3% of valid votes—which includes blank ballots—being applied. Parties not reaching the threshold are not taken into consideration for seat distribution.
Registered parties and federations of parties are allowed to field candidates, as well as party alliances formed within 10 days from the Cortes' dissolution. Additionally, groups of electors—a legal figure in Spain referring to temporary associations of citizens grouped for the sole purpose of contesting a particular election—are required to obtain the signatures of at least 1% of registered voters in the district in order to be able to field candidates. Since 2011, parties, federations of parties and coalitions left out from the Congress in the previous election are also required to obtain the signatures of at least 0.1% of registered voters in the districts they intend to contest. No party, federation, coalition or group of electors may field more than one list of candidates per district for the same election, and member parties of a contesting federation or alliance are barred from fielding their own lists. From 2002—and in compliance with the Political Parties Organic Law 6/2002—fielded candidates are also forbidden from continuing or succeeding the activities of judicially illegalized, dissolved, or suspended political parties.