The clash between South Korea's ruling party and the main opposition intensified on Tuesday over whether Acting President Han Duck-soo possesses the authority to approve three new Constitutional Court justices, a move that could lower the threshold for President Yoon Suk Yeol's impeachment to be confirmed by the court.

An incumbent president's impeachment would require decisions in favor from at least six justices at the Constitutional Court. Given that there are currently six justices and three seats remain vacant, Yoon would not be impeached without a unanimous decision by all incumbent justices.

Against this backdrop, the ruling People Power Party's floor leader Rep. Kweon Seong-dong argued Tuesday that the acting president Han, who doubles as the Prime Minister, was not endowed with the power to nominate new judges to any court as long as Yoon remains suspended from his position.

"The acting president may exercise a wide range of presidential executive powers and (Han) is supposed to do so. But an acting president's use of the power to approve a court justice is deemed legitimate when the presidential office becomes vacant, not when the incumbent is suspended," said Kweon, a self-proclaimed pro-Yoon Suk Yeol figure, in a meeting with party lawmakers.

The National Assembly has the power to recommend justice nominees to fill vacancies on the Constitutional Court. The nominees go through a parliamentary hearing, but presidential approval is required for them to take office.

Kweon, a five-term lawmaker, cited a precedent in which Hwang Kyo-ahn, then as acting president, approved the nomination of a new Constitutional Court justice in March 2017 after former president Park Geun-hye's ouster.

"Back when Hwang was acting president during Park's impeachment, the Democratic Party criticized Hwang for undermining democracy by attempting to approve a new Constitutional Court justice," Kweon said. "Now the party has completely changed from its previous stance."

The main opposition countered Kweon's remarks.

Democratic Party of Korea's Floor Leader Rep. Park Chan-dae on Tuesday said Han's approval of the justice nominees would be in accordance with the Constitution. Han's decision to fill the three vacant seats would enhance the fairness and trustworthiness of the trial that could finalize the impeachment of Yoon, accused of insurrection through his Dec. 3 imposition of martial law, he added.

He also condemned Kweon's argument as a "foul scheme by the ruling party to delay (Yoon's impeachment trial)," in a separate meeting immediately after Kweon's remarks.

But he said Han's possible exercise of the veto power to strike down opposition-sponsored bills would be illegitimate and would "trigger an endless political conflict."

The confrontations over the acting president's authority to appoint Constitutional Court justices came amid rising tensions over an opposition party's plan to push for a parliamentary confirmation hearing for three justice nominees.

Rep. Kim Han-kyu of the Democratic Party told reporters Monday he expected that a confirmation hearing on three nominees -- one recommended by the ruling party and two by the opposition -- is tentatively scheduled for Dec. 23-24. The ruling party, however, denied that claim, saying no agreement between the parties has been reached.

Meanwhile, the Constitutional Court stated that it had yet to confirm whether President Yoon received documents from the court requesting a written response within seven days.

“The documents are in the process of being delivered to the president,” said Lee Jin, spokesperson for the Constitutional Court, adding that the presidential office has not provided any confirmation as to whether he has received it.

If the documents are not delivered, there will be delays in subsequent proceedings.

This raises concerns that President Yoon's legal counsel may not attend the preparatory procedures scheduled for the 27th, or may claim, if they do attend, that they didn't receive the documents.

Yoon hasn't given any notice of his legal representation to the Constitutional Court. He has similarly refused to receive a summons sent to his residence by the joint investigative unit probing the insurrection charges.

The court spokesperson also said the court has decided not to livestream Yoon's impeachment trial proceedings.

Asked whether the acting president can appoint justices to the three vacant seats, Lee said, "There have been past instances, such as when Acting President Hwang Kyo-ahn made appointments.”

Constitutional Court Justice Kim Hyung-du also told reporters on Monday morning he expected the formation of a nine-member court before the end of the year.