From left, Constitutional Court of Korea justices Moon Hyung-bae, Lee Mi-son, Kim Hyung-du, Jung Jung-mi, Cheong Hyung-sik and Kim Bok-hyeong / Captured from the website of Constitutional Court

The final decision on President Yoon Suk Yeol's impeachment now rests with the Constitutional Court, following the National Assembly's passage of a motion, Saturday, to oust him over his declaration of martial law.

Under the law, when the Assembly passes an impeachment motion against a president, the court is required to review and decide whether to uphold or reject it within 180 days.

The situation is complicated by the fact that the court currently has only six justices out of nine, as three vacancies remain unfilled following the retirement of former justices in October. Although the Assembly was supposed to nominate replacements, it has so far been unable to do so.

Under a clause of the Constitutional Court law, a case can be reviewed when at least seven justices are present.

However, Korea Communications Commission Chairwoman Lee Jin-sook, who was impeached by the Assembly in September, filed for an injunction to suspend that clause, so the court could continue reviewing her impeachment case. The court granted the injunction, temporarily suspending the clause and permitting reviews of both her case and others.

As a result, the court is technically able to review Yoon's impeachment case.

The law also stipulates that at least six justices must approve an impeachment for it to be upheld, meaning the Assembly's motion to remove Yoon can be validated if all six justices unanimously agree.

However, a decision upheld by only six justices could face legitimacy concerns due to the gravity of the issue. In the 2004 impeachment case of then-President Roh Moo-hyun, all nine justice positions were filled, and in the 2017 case of then-President Park Geun-hye, the court was composed of eight judges.

If the six justices make a decision this time, there is a possibility that some may not accept the court's ruling, particularly if it goes against their preferences.

Eight Constitutional Court judges make a ruling on then-President Park Geun-hye's impeachment in Seoul, March 10, 2017. Korea Times file

The situation has led to growing calls to prioritize filling the court vacancies.

Recently, the main opposition Democratic Party of Korea recommended two justice candidates, while the ruling People Power Party proposed one. If the Assembly conducts the confirmation hearings and approves the nominations, the vacancies can be filled soon.

However, even in that case, the final appointment rests with the president. Since Yoon is suspended from duty following impeachment, the question arises as to who has the authority to make the appointments.

Some argue that Prime Minister Han Duck-soo, who is currently acting as president, has the authority to appoint new justices.

However, the opposition is also seeking to impeach Han, arguing that he is responsible for the martial law fiasco, as he attended a Cabinet meeting prior to Yoon's declaration of martial law.

Even if Han avoids impeachment and remains acting president, it is uncertain whether he will use his presidential authority to appoint justices. During the 2017 impeachment review of Park, then-acting President Hwang Kyo-ahn refrained from appointing a justice to fill the vacancy.

Upon the Assembly's vote, the court's acting President Moon Hyung-bae said, "We'll conduct a swift and fair review." The court plans to hold a meeting on Monday and decide which justice will be in charge of the case.