Kim Dong-cheol, the party's floor leader, said that the boycott will continue unless Choo Mi-ae, the leader of the ruling Democratic Party, takes "convincing" measures such as stepping down from her post and issuing an official apology.

"From today onward, we will not cooperate with any parliamentary proceedings if Choo does not take convincing steps," Kim told reporters.

Earlier in the day, Choo said that the opposition party's probe result that found no evidence implicating its former presidential candidate Ahn Cheol-soo and former leader Park Jie-won in the scandal appeared to be an attempt to contain its fallout.

The in-house probe was launched after a rank-and-file party member was accused last month of fabricating an election-season allegation that President Moon Jae-in's son landed a job at a public agency in 2006 thanks to his father's influence.

The boycott could hamper parliamentary procedures for top Cabinet nominees and the passage of pending bills, including one on an 11.2 trillion won ($9.9 billion) extra budget the government has pushed to mainly create jobs in the public sector.

The People's Party with 40 lawmakers is seen as holding a "casting vote" in key legislative affairs at a time when there is no party enjoying a majority at the 299-member National Assembly. The ruling party has 120 seats.

The latest scandal has eroded public confidence in the party, which was launched early last year under the leitmotif of "new, clean" politics in a complete break from "outmoded, corruptive" partisan practices. (Yonhap)