The upper house of parliament is a largely ceremonial chamber and much less powerful than the lower house, which chooses the prime minister

 

Nonetheless, with half the upper house's 242 seats up for grabs, a humiliating loss for the Liberal Democratic Party could prompt party leaders to urge Abe to resign.

 

Scandals

 

Abe's government has been rocked by a series of scandals in recent months that have forced three ministers from his cabinet, two by resigning and one by suicide.

 

One cabinet minister resigned in December over a political spending scandal, the health minister barely kept his post after referring to women as "birth-giving machines", and the scandal-tainted farm minister hanged himself in May.

 

Then last week the defence minister stepped down over remarks that appeared to condone the 1945 US atomic bombings of Hiroshima and Nagasaki.

 

And in the latest scandal Norihiko Akagi, Abe's agriculture minister, is under fire over allegations that he falsely booked millions of yen in spending for political offices that no longer exist.

 

Buoyed by Abe's plunging popularity the main opposition Democratic Party are touting the upper house poll as a step towards taking power.

 

"A huge political battle has begun that will become the first step towards greatly altering our country's politics," the party said in a statement as campaigning began on Thursday.