MADRID (Reuters) - Four decades of two-party dominance in Spain may begin to unravel on Sunday, as voters turn to anti-corruption and anti-austerity candidates after a seven-year economic slump.
The ruling centre-right People's Party and opposition Socialists - who have essentially shared power since the end of Francisco Franco's dictatorship in the 1970s - are likely to have their worst showing in a European election in 25 years, opinion polls show.
Their poor showing may foreshadow fragmentation in the general elections due by early 2016. If so, politicians may be forced to form Spain's first coalition government to push through reforms aimed at keeping the economy on track.
High-level corruption, deep cuts in public spending as the government dodged a debt default and a jobless rate of one in four have all soured Spanish voters on the two-party system.
However, they are not turning to the sort of anti-immigrant or Eurosceptic parties that are gaining ground elsewhere in Europe and are expected to double their presence and take a quarter of the European Parliament.
Political scientists and sociologists say Spanish voters are just as skeptical about Europe as other Europeans, out of disgust with the response to the economic malaise. But they are also wary of populist and xenophobic messages. Many of them remember life under fascism, and many had family members who emigrated in the 1960s and '70s in search of work.
"In Spain, there's an oversupply of pro-Europe parties," said Jose Ignacio Torreblanca a senior fellow with the European Council for Foreign Relations. "If you want to vote anti-European establishment, even the smaller parties in Spain are pro-Europe."
Surveys of voters show the Socialists and the PP losing around 10 of their combined 47 seats in the European Parliament, where Spain has 54 seats in total. The United Left - which includes the former Communist party - will triple its seats to six. The social-liberal Union for Progress and Democracy, or UPyD, could jump to four seats from one.
"Spain needs to rethink the two-party nature of its political system. If the smaller parties gain representation, we'll be seeing an effect on the big parties - especially the opposition will have to change course," said Antonio Garcia Tojar, sociology professor at Madrid's Complutense University.
Voter alienation is high. The PP's leaders are being investigated for financial misfeasance and Socialists in the southern region of Andalucia are accused of skimming jobless benefits, while taxpayers foot the bill for bailing out banks that loaned recklessly to developers in league with politicians.
A number of colorful fringe candidates - including a Franco-Italian tax-fraud whistleblower and a judge charged with abuse of power after he threw a prominent banker in jail - have tapped into the disenchantment. They are not expected to glean enough votes for a seat in the European legislature, though.
The most successful newcomers are the leftist group Podemos - "We Can" in English - which polls show winning one or two seats. The two-month-old party is fielding young candidates new to politics and trying to tap the anti-establishment sentiment of the "Indignados" movement that occupied Spanish plazas three years ago and called for a new political model.
Perhaps most emblematic of the discontent is the Empty Seats movement, which aims to win a seat in the European legislature, then not fill it.
"People can use their vote to leave the seat empty. Or, if you want to look at it another way, they can throw politicians out of the institutions ... For the first time citizens can lay off the political class," said Luis Prado, a pharmacist who is the lead candidate for Empty Seats but won't actually serve if his party wins a seat.
But not even the upstart anti-establishment parties can halt the rising tide of abstention in Spain. Participation is expected to fall as low as 40 percent, down from 47 percent in the last European election, according to Metroscopia polling firm. That reflects a reality around Europe.
"Everything is going to hell and I don't see an option that can change that," said 26-year-old Hector, who earns 700 euros a month working part-time at a number of jobs - cleaning a night club, waiting tables, and working at a gym. Hector did not want his last name published.
"I thought about voting United Left or the other smaller parties, but I don't think the European elections can change our situation much."
Almost half of Spain's 18-25 year olds who want to work cannot find jobs.
Political analysts say Spain's electoral system - which is not strictly proportional - will limit the erosion of the two-party system.
Electoral rules were designed to foster stability by giving the most-voted-for parties bonus seats in general elections. That makes it hard for new parties to build momentum. But the stable democracy that was cherished after Franco's dictatorship is now generating frustration among voters who are eager for alternatives and electoral reform.
"The two-party system was surely conceived as a way to protect democracy but now it may be becoming an obstacle for democracy," said Tojar.
Additional reporting by Catherine Macdonald; Writing by Fiona Ortiz; Editing by Julien Toyer