Millions of Europeans still feeling the hangover of a prolonged economic slump began voting Thursday in a four-day, 16,000-candidate election that is intended to draw the continent together — but is likely to strengthen those seeking to pull it apart.

Although parties on the center-right and the center-left are expected to hold on to their majority in the European Parliament, those on the extremes are poised for a substantial boost, with voters rallying to the message of blaming Brussels for years of high unemployment and sluggish growth.

The election, held every five years, gives voters their only direct say in who governs the
28-member European Union. It comes as Europe struggles to remain united amid a major security challenge posed by Russia’s meddling in Ukraine and a continuing economic malaise that has forced the continent to bind together more tightly than ever before.

But if the prescription for economic recovery has been ever-closer integration, large numbers of voters are rejecting the medicine, choosing parties that preach national sovereignty over shared decision-making.

“It’s a populist backlash against a technocratic project,” said Mark Leonard, director of the European Council on Foreign Relations. “The mainstream parties have been complicit in what’s happening with the E.U., and now voters want to give them a bloody nose.”

Public opinion polls suggest that they will do exactly that, with parties that are hostile toward Europe expected to win between a quarter and a third of seats in the 751-member parliament. Voting began Thursday in Britain and the Netherlands, and it will continue across the continent through Sunday, with results expected late that evening.

Preliminary tallies late Thursday and early Friday were mixed. A Dutch exit poll showed the far-right Party for Freedom doing unexpectedly poorly and finishing in fourth; the populist U.K. Independence Party appeared to be gaining seats in local English elections.

Parties on the far right and the far left are not expected to do well enough to advance their legislation or to create gridlock in the European parliament, where bills can pass with a simple majority.

But the vote could hold major ramifications for domestic politics in some countries and bring a sense of political instability back to the region. It could also influence the choice of a new European Commission president, which the parliament will have to approve for the first time.

According to the polls, anti-
establishment parties are doing particularly well in countries suffering the worst aftereffects of Europe’s debt crisis, with a toxic cocktail of high unemployment and austerity poisoning the political atmosphere.

In countries such as Greece, Italy and to some extent France, the voter backlash also seems partly aimed at Germany’s economic leadership in the region — particularly Berlin’s push for balanced budgets among its economically weaker neighbors.

“Underpinning this vote is a sense of economic insecurity, rising unemployment, social benefits being cut and a shrinking public sector even as you have seen migration waves in some countries,” said Wolfango Piccoli, managing director of the political risk assessment firm Teneo Intelligence. “These anti-establishment parties are able to capitalize on this insecurity.”

In Greece, the leftist Syriza party is leading in several polls. Coming off a strong showing in recent regional elections, such a boost could put renewed pressure on the center-right government of Prime Minister Antonis Samaras to back away from reforms and possibly even hold early elections. Syriza’s charismatic leader, Alexis Tsipras, is an anti-austerity crusader who has vowed to rewrite Greece’s international bailout, and his rising popularity is renewing some market jitters.

In Italy, the election is being seen as a referendum on Prime Minister Matteo Renzi’s first three months in office. But in recent weeks, the anti-establishment Five Star Movement of comedian Beppe Grillo has been rising in the polls. If Grillo’s left-leaning party beats Renzi’s Democrats to emerge as Italy’s top vote-getter, the result would come as a major blow to the government and could put the brakes on the prime minister’s pledge to reform the stagnant Italian economy.

The anti-establishment wave hasn’t been limited to Europe’s struggling south; the stronger economies of the north have felt it, too.

In Germany, for instance, the Alternative for Germany (AFD) party, launched last year, advocates that economically weaker countries such as Greece should pull out of the euro zone, or that Germany should if they don’t.

But the party has desperately sought to separate itself from the “far-right” label, which, given German history, is seen as a political kiss of death.

Hans-Olaf Henkel, a top AFD candidate, said that French nationalists in particular had dangerously mixed far-right, anti-immigrant positions with traditionally leftist policies that envision a big state controlling the national economy.

National Front leader Marine Le Pen “has combined nationalism and socialism, and when you do that, you get something that is very well known in the history of Germany,” Henkel said. “So, no, we want nothing to do with her.”

At home, AFD has nevertheless faced an onslaught of criticism for being exactly what it says it is not — far right. Henkel insisted that such categorizations were the product of unfair tactics being used by mainstream parties to paint a potential rival as fringe.

But such parties can sometimes be their own worst enemies, and statements by some AFD candidates, particularly on immigration, have not sounded much different than those by people considered extremists.

The same has been true of the U.K. Independence Party, which has faced renewed criticism in recent days after party leader
Nigel Farage said in a radio interview that he would not want to live next door to Romanians.

Farage later backtracked from the comments, but UKIP has repeatedly warned of the dangers of Eastern European gangs bringing criminality to peaceable British towns and cities. The talking point has helped propel UKIP to the lead in pre-election polling, and it was clearly on the minds of voters who cast ballots Thursday.

“I don’t like the way Europe’s dominating this country,” said Dennis Hayzer, 67, a maintenance supervisor who switched his allegiance to UKIP after a lifetime of supporting the Conservatives. “I’m not a racist, but the drunks on the street corner tend to be Eastern European. The crime in the area — it tends to be the Eastern Europeans. So I just think they’ve got to curb the influx of immigrants and do more to help the people who are already here.”

Faiola reported from Berlin.