The National Assembly's Legislation and Judiciary Committee Chair Rep. Jung Chung-rae, left, argues with committee members from the ruling People Power Party, who questioned the hearing's legality at the National Assembly in Seoul, Friday. Yonhap

Rival parties clashed again, Friday, at the first hearing on an online petition calling for President Yoon Suk Yeol's impeachment over his alleged interference in a military investigation into a Marine's death.

The ruling People Power Party (PPP) claimed the hearing, led by the National Assembly-dominating main opposition Democratic Party of Korea (DPK), and the impeachment petition itself are "unconstitutional and illegal" because the key issues cited as the justification for impeachment stated in the petition are groundless. But the DPK pushed ahead with the hearing, and said it would file a complaint over nine witnesses who refused to attend the hearing.

The Assembly's Legislative and Judiciary Committee held the hearing after an online petition seeking Yoon's impeachment gained more than 1.4 million consents from citizens.

One of the key issues the committee discussed Friday was Yoon and other presidential aides' alleged exercise of influence on the military's investigation into a Marine's death last year. The hearing took place on the first death anniversary of the fallen Marine, Cpl. Chae Su-geun, who died during a search mission for victims during heavy rainfall.

It has been alleged that the presidential office interfered with the investigation to protect Lim Seong-geun, who was the commander of the Marine Corps 1st Division at the time of the incident, from punishment.

The hearing had a rocky start as the PPP attempted to block entry to the meeting room at the Assembly. The ensuing confrontation between the rival parties resulted in a brief physical clash, and Rep. Jeon Hyun-heui of the DPK sustained a slight facial injury.

Lawmakers from the ruling People Power Party (PPP) stage a protest in front of the meeting room of the National Assembly's Legislative and Judiciary Committee at the National Assembly in Seoul, Friday, condemning the opposition's forceful push for a hearing on a petition calling for the impeachment of President Yoon Suk Yeol. Yonhap

While the committee had requested 22 witnesses to attend the session and answer lawmakers' questions on the the allegations, including former Defense Minister Lee Jong-sup, incumbent Defense Minister Shin Won-sik and National Intelligence Service (NIS) Director Cho Tae-yong, nine of them, including Shin and Cho, submitted reasons for their absence.

Particularly, Lee Jong-ho, the former CEO of Black Pearl Investment who is a person of interest in the allegations, did not attend the session. Lee was convicted last year for his involvement in a stock price manipulation scheme related to Deutsche Motors — a separate allegation involving first lady Kim Keon Hee — and it is alleged he moved to save Lim by using his connection to the first lady.

During the session, Lim reiterated that he does not know Lee Jong-ho.

"I don't know him. I've never met him. I only learned through the media that such a person exists," Lim said.

Former Marine Corps 1st Division Commander Lim Seong-geun, front, takes the witness oath during a hearing at the National Assembly in Seoul, Friday. Yonhap

The issue surrounding the death of the Marine has become one of confrontational political bickering between the rival parties.

The DPK-dominated Assembly pushed a bill mandating a special counsel investigation into the allegation — first in the previous 21st Assembly and second in the current 22nd — but Yoon vetoed both of them.

The legislative committee plans to hold its second hearing on the impeachment petition next Friday. The focus of the next session will be the allegations related to the first lady's acceptance of a luxury handbag from a pastor and the Deutsche Motors stock manipulation case. A total of 23 witnesses have been selected, including Kim's mother, as well as Prosecutor General Lee One-seok.

Meanwhile, the presidential office reaffirmed its stance regarding the hearings, stating that the office "will not compromise on issues that are potentially unconstitutional or illegal."