The opposition's boycott of Diet deliberations entered its second day Tuesday as the ruling camp offered no concessions over its plan to revise the House of Councilors election roster system.

Members of the four major opposition parties boycotted Tuesday's Lower House session, insisting they will not attend deliberations of most Diet committees unless the ruling bloc retracts its "hardline" attitude on the issue.

The boycott started Monday as the ruling triumvirate -- the Liberal Democratic Party, New Komeito and the New Conservative Party -- opened an Upper House special committee to legislate its planned revision of the roster system.