The Christian Social Union (CSU) -- a conservative sister party to Merkel's Christian Democrat Union (CDU) -- has dominated Bavarian politics for almost seven decades. Apart from a three-year period in the 1950s, the party has continuously governed the state since 1949.
At this election, however, the CSU could lose votes to the anti-immigration, far-right Alternative for Deutschland (AfD) party and to the left-wing, environmentalist Greens.
|Chancellor Angela Merkel. Photo: Reuters.
CSU lawmaker Robert Brannekaemper told CNN he was still optimistic the party would retain enough votes to come out ahead, even if it loses support to what he described as a "counter-trend of populism."
"Bavaria is a safe and rich state, with the lowest unemployment in the country. We ought to get 60%," he told CNN. "But there is also a counter-trend in Europe. Italy, France, Holland -- everywhere. Considering this, we hope to get 40%, as a top result."
The state bore the brunt of the 2015 refugee crisis. At its peak, thousands of asylum seekers were crossing into Bavaria every day. Since then, both Merkel and her CSU allies have been criticized for their management of the influx.
How the CSU fares on Sunday will determine whether the party leadership stays or goes and could have a knock-on effect to Merkel's cabinet, particularly if Minister of Interior and CSU party leader Horst Seehofer is forced to resign.
On October 28, regional elections in Hesse could deal an additional blow to the Chancellor. If both regional elections show voters continue to flee the CDU-CSU alliance, Merkel will come under pressure to resign as party leader at the CDU party conference in December.
A poll released just before the Bavaria vote showed nationwide dissatisfaction with the mainstream parties of Merkel's governing coalition. The CDU/CSU and center-left Social Democratic Party suffered record lows of 26% and 15% respectively, while the Greens and AFD have surged to 17% and 16%.
Merkel suffered a severe blow last month when her party members voted out Volker Kauder as CDU parliamentary group leader. He was the man Merkel trusted to keep the party in line for the last 13 years.
"The next three months will be decisive in German politics," explains political scientist, Timo Lochocki. "It's difficult to imagine she [Merkel] will serve the entire term. The odds are very high that she will be forced to step down next year or in 2020. It's clear she lacks the support of 50% of her MPs and the pressure is insurmountable."