The outcome of an election to the European Parliament will have important political implications for governments in some European Union member states.
Who are likely to be the winners and losers?
Britain's ruling Labour Party looks set to suffer a crushing defeat in the European Parliament election. Some polls suggest it may finish in an embarrassing third place, far behind the Conservatives and Liberal Democrats, the two other main parties.
Opinion poll findings highlight the damage inflicted on Labour by a scandal over lawmakers' perks and increase speculation over the future of Prime Minister Gordon Brown, forced to reshuffle his cabinet after ministerial resignations. There is speculation Brown could face a leadership challenge if results are particularly bad.
President Nicolas Sarkozy's UMP party is expected to emerge on top on Sunday, with the latest polls predicting it will win 27 percent of the vote against 20 percent for the Socialists. It is rare in France for a ruling party to do well at mid-term elections and Sarkozy will hope to use the ballot as evidence the French support his reform program.
His main worry is that the cumulative vote for center-left and far-left parties is expected to be much higher than the UMP score, suggesting he would struggle if they joined forces.
The European Parliament election is seen as a test case for Germany's federal election in September, in which conservative Chancellor Angela Merkel hopes to be re-elected. A survey conducted last month showed 37 percent of voters intended to vote for Merkel's Christian Democrats (CDU) in the European election, giving it a clear lead over the SPD, which has been forecast a vote of 28 percent.
The SPD has ruled in an uneasy grand coalition government with the CDU for the past four years and struggled to convince voters of its policies and leadership skills in the financial crisis. A poor performance in the European election could further weigh on the party's image with voters, analysts say.
Support for Ireland's governing party, Fianna Fail, is at a record low and Prime Minister Brian Cowen could face a threat to his leadership. In one opinion poll the party dropped to third place behind its main rivals, Fine Gael and Labour, despite Cowen telling voters Ireland's economy would recover quickly when the global crisis ends.
With Ireland set to vote again on the EU's Lisbon reform treaty later this year, the performance of Libertas -- one of the leading groups whose campaign helped defeat the treaty in a first referendum last June -- will be significant. Polls show leader Declan Ganley is the only Libertas runner with any real shot at landing a top job in Brussels.
Despite a string of scandals such as alleged bribes to a lawyer, a relationship with an 18-year-old woman and the use of state planes, Prime Minister Silvio Berlusconi's center-right party is expected to win about 40 percent of the vote and come away as the largest party, according to opinion polls.
Despite the economic recession, Berlusconi remains Italy's most popular politician by far and the opposition suffers from being split among a diverse spread of left-leaning, anti-corruption and Catholic groups.
Spain's governing Socialists are widely expected to lose, but not heavily, to the Conservative opposition Popular Party -- with polls suggesting a PP lead of 0-4 percentage points.
Given the dire state of the economy, with unemployment at about 18 percent, this range of results would probably constitute no major disaster for Prime Minister Jose Luis Rodriguez Zapatero.
Polls show the ruling conservative party -- which is struggling with the economic crisis, social unrest and numerous scandals -- losing to the main opposition socialist party.
With an early parliamentary election looming in the next nine months, Greek parties see the EU vote as a precursor to the national vote and all will have their eyes on the gap between the two parties.
The two biggest parties in the Czech Republic -- which holds the EU presidency until the end of this month -- are neck and neck in surveys before the European election, which will be an important test before a parliamentary election in October.
Polls show the former ruling right-wing Civic Democrats may win the two elections but be unable to form an alliance with a parliamentary majority, which could open the way for a minority Social Democrat government backed by the far-left Communists.
Hungary's Socialists, who rule in a minority government led by Prime Minister Gordon Bajnai, are expected to suffer a crushing defeat to the main opposition party Fidesz. In a recent poll, Fidesz was seen winning 14-16 seats, the Socialists five to six and the far-right Jobbik party was expected to win one of the 22 seats on offer.
Political analysts say a big victory for the opposition would make an early parliamentary election more likely.
Bulgaria's ruling Socialists are likely to suffer a defeat because of public anger over its failure to tame chronic corruption and organized crime as well as act to protect the economy from the global economic crisis. Opinion polls show the right-wing opposition GERB, led by Sofia's straight-talking Mayor Boiko Borisov, winning five to six of the total 17 seats.
The vote is expected to be a litmus test for the Balkan country's parliamentary election on July 5, in which polls suggest the Socialists will be ousted.
Latvia's ruling coalition is made up of five parties and polls show only two of them will beat the five percent barrier required to win European Parliament seats -- the New Era party of Prime Minister Valdis Dombrovskis and the smallest coalition party, Civic Union. This would be another blow as the government faces a currency crisis.
The largest opposition party the Center Party is set to win most seats in the election, opinion polls show. The win could boost the party's confidence before local elections in October, but is not expected to herald a government crisis.