Sofia  - Some 6.9 million Bulgarian voters are eligible to cast ballots Sunday in the country's first parliamentary poll since it joined the European Union in 2007.

Surveys indicated an uphill struggle for Prime Minister Sergei Stanishev's Socialist Party (BSP) after its popularity dipped owing to corruption scandals and economic hardship, and it is predicted to win only between 17 and 22 per cent of the votes.

Sofia Mayor Boyko Borisov's GERB party, still untested in parliamentary polls and riding a "clean hands" campaign, was predicted to win most votes - between 26 and 32 per cent.

A junior partner in Stanishev's coalition, the Movement for Rights and Freedoms, was expected to remain stable with the votes of the 10 per cent Turkish minority.

The other party in the outgoing coalition, abdicated King Simeon II's National Movement, may struggle to win the minimum 4 per cent required for parliamentary repsresentation.

Tipped to cruise past that hurdle were the fiercely nationalist, anti-European Ataka party and the centre-right Blue Coalition, and possibly a small new party called Order, Law and Justice.

Voting starts at 6 am and ends at 7 pm (0300-1600 GMT), expected to be followed by exit polls. Because of the complex mixed-electoral system, first trustworthy results are not expected before Monday.

Bulgaria joined NATO in 2004 and the EU three years later, but remains plagued by poverty and widespread corruption, which last year spurred Brussels into suspending or scrapping a billion dollars' aid.(dpa)