Opposition lawmakers returned to Diet deliberations Friday, ending a nearly three-week boycott after the House of Councilors passed a controversial bill to revise the electoral system the previous day.

The bill, which changes the proportional representation roster system for Upper House elections, was sent to a Lower House committee Friday despite calls from the opposition for the measure to be thoroughly deliberated..

Naoto Kan, secretary general of the Democratic Party of Japan, announced that the DPJ is ready to submit a counterproposal to the Lower House.

The bill proposed by the ruling bloc -- the Liberal Democratic Party, New Komeito and the New Conservative Party -- will allow an Upper House candidate to receive votes cast for other candidates registered on the same party roster.

The opposition claims the plan will encourage popularity votes.

LDP Secretary General Hiromu Nonaka lashed out at Kan, claiming the DPJ's move to submit a counterproposal now, after refusing to debate the ruling camp's bill for weeks, lacks consistency.

Nonaka also said the DPJ should not submit a new bill to the Lower House and ask for fresh deliberations there because the issue concerns the voting system for the Upper House. The DPJ's counterproposal would effectively abandon the current Upper House proportional representation system.

The opposition camp meanwhile said it hopes in Diet sessions to pursue a series of recent LDP scandals, including one involving Chief Cabinet Secretary Hidenao Nakagawa.

Recent media reports allege that Nakagawa, Mori's right-hand man, lied in Diet sessions about his relationship with a rightist figure who revealed Nakagawa's alleged extramarital affair with a Tokyo hostess.