The passage came after the rival parties reached a compromise to break the long-running parliamentary impasse last week. Under the deal, the ruling Democratic Party agreed to an independent counsel probe into the scandal while the main opposition Liberty Korea Party agreed to pass the supplementary budget.
The scandal centers on allegations that a power blogger, known by his nickname Druking, and his team manipulated comments on Internet news stories in an effort to sway public opinion on hot-button political issues and that ex-Rep. Kim Kyoung-soo of the ruling party knew and had communicated with Druking.
It will be the first independent counsel probe since the administration of President Moon Jae-in took office last year and the 13th such investigation in Korean history. The previous special counsel investigation was conducted in December 2016 into a corruption scandal that led to the ousting of former President Park Geun-hye.
Under the bill, a special probe team will be given as long as 90 days for the inquiry.
The team is expected to zero in on Druking and his team's alleged illegal online opinion manipulation and their use of funds that are suspected of having been created in an illicit manner.
The bill calls for a national bar association to field four special prosecutor candidates before three opposition parties recommend two of them to President Moon. Moon is required to select one of them as a special prosecutor.
The team also includes three assistant independent counsels, 13 prosecutors and 35 inspectors. It is expected to launch a probe after local elections slated for June 13.
The now-jailed Druking claimed last week that the ex-lawmaker tacitly agreed to his campaign for the online opinion rigging. Kim, who has close ties with President Moon, flatly denied the allegations, dismissing the letter as a "fiction."
Fresh reports revealed Monday that Druking had met another confidant of President Moon, Song In-bae. Song has admitted to meeting Druking at least four times, but denies any prior knowledge of the opinion rigging attempts.
The extra budget bill, meanwhile, is aimed at creating new jobs for young people and boosting regional economies suffering from restructuring in the shipbuilding and the auto-making sectors.
The number of new jobs was slightly above the 100,000 mark for the third straight month in April, the worst record since the 2008 global financial crisis, according to government data.
The bill was the second of its kind under the administration of President Moon Jae-in. Last year, the National Assembly approved an 11 trillion won supplementary budget.
In March, the government proposed an extra budget worth 3.9 trillion won, but during a parliamentary review, the amount was curtailed by a net 21.8 billion won. (Yonhap)