Aso says he plans to dissolve the parliament Tuesday.
Meanwhile, a petition reportedly has been signed by more than one-third of the Liberal Democratic Party's MPs, demanding a urgent meeting with hopes of heading off Aso.
The prime minister has been under pressure to step down for some time. Aso has promised to call an election for Aug. 30 but critics say that would be political suicide.
Aso's Liberal Democratic Party has been in power for almost half a century but many in his party now see him leading them to defeat.