BERLIN (Reuters) - Chancellor Angela Merkel's Bavarian allies are heading for their worst state election result in over 60 years in a regional vote on Sunday that is likely to increase tensions within Germany's fragile coalition government.
According to the latest polls, the Christian Social Union (CSU) will win around 34 percent, losing the absolute majority with which the center-right party has controlled its southeastern heartland for most of the post-war period.
Voting stations open at 8 a.m. (0600 GMT) and broadcasters are expected to publish exit polls shortly after 6 pm (1600 GMT).
One of the biggest winners are likely to be the ecologist, pro-immigration Greens who are projected to more than double their vote share to up to 19 percent and overtake the center-left Social Democrats (SPD) as the second-strongest party.
The regional protest party Free Voters and the anti-immigration Alternative for Germany (AfD) party are both forecast to win roughly 10 percent of the votes.
This could complicate CSU State Premier Markus Soeder's efforts to form a stable coalition government in Bavaria.
The splintered electoral result could force Soeder, who has ruled out a coalition with the AfD, into an awkward alliance with the left-of-center Greens.
Horst Seehofer, CSU party leader and interior minister in Merkel's federal government, could face calls to give up at least one of his posts following the Bavarian election as his hard-line rhetoric against asylum seekers is likely to scare away voters.
"We've lost trust because of the CSU," Volker Bouffier, deputy party leader of Merkel's Christian Democratic Union (CDU), told Welt am Sonntag newspaper. He accused Seehofer of damaging the image of the CDU/CSU conservative alliance.
Bouffier is premier in the state of Hesse where another regional election will be held later this month.
Seehofer has been among Merkel's fiercest critics following her decision in 2015 to welcome more than 1 million migrants. He has gradually shifted the CSU, the sister party to the CDU, to the right to counter the rise of the AfD party.
Divisions between the conservative allies have widened further since March, when an inconclusive national election forced them into a coalition with the left-leaning SPD.
Merkel's fourth and probably final government has already come close to collapsing twice, in arguments over immigration and a scandal over Germany's former domestic spymaster. The parties are also at odds over how to phase out polluting diesel cars and whether to grant tax cuts for the rich.
(Reporting by Michael Nienaber; Editing by Clelia Oziel)