Japan is voting in upper house elections on Sunday in a poll that is seen as a referendum on 10 months of rule by the Democratic Party of Japan (DPJ).
Prime Minister Naoto Kan told supporters on Saturday that Japan had to avoid financial collapse.
Sagging support for the Democratic Party of Japan, which surged to power for the first time last year, rebounded after Mr Kan replaced his indecisive predecessor Yukio Hatoyama last month.
But ratings slipped again after he suggested raising the sales tax to curb public debt and struggled to persuade voters he had a clear plan to fix Japan's woes.
Mr Kan says tough decisions are vital to avoid a Greek-style debt crisis, since Japan's public debt is already close to twice the size of the nearly $7 trillion economy.
The DPJ came to power last August, ending half a century of dominance by its main rival, the conservative Liberal Democratic Party.
Half of the upper house is being contested in Sunday's poll - a total of 121 seats.
Currently, the DPJ and its coalition ally, the People's New Party, control 122 seats.