The push to impeach Prime Minister Han Duck-soo, who has been acting president since Yoon was impeached on December 14 for declaring martial law, has thrown South Korea's once-vibrant democratic success story into uncharted territory.
Ahead of the parliamentary session, opposition leader Lee Jae-myung said his Democratic Party, which has majority control of parliament, will go ahead with the plan to impeach the acting president, accusing Han of "acting for insurrection".
"The only way to normalise the country is to swiftly root out all the insurrection forces," Lee said in a fiery speech, adding the party was acting on the public order to eradicate those who have put the country at risk.
A court will decide if Yoon Suk-Yeol will be reinstated or permanently removed from office. (AP PHOTO)
There has been overwhelming public support for Yoon's removal, according to opinion polls conducted after his martial law attempt.
The plan for a vote to impeach Han was unveiled on Thursday by the main opposition Democratic Party after he declined to immediately appoint three justices to fill vacancies at the Constitutional Court, saying it would exceed his acting role.
If Han is suspended, Finance Minister Choi Sang-mok will assume the acting presidency by law.
Lee's pledge to oust Han came minutes after Choi warned that impeaching the acting president would seriously damage the country's economic credibility and asked political parties to withdraw the plan.
"The economy and the people's livelihoods are walking on thin ice under a national state of emergency and it cannot cope with any greater political uncertainty that will result from another acting president assuming the acting presidency," he said.
The South Korean won weakened to a fresh low of 1,486.7 per dollar on Friday, the weakest since March 2009, as analysts said there was little to reverse the negative sentiment stemming from the political uncertainty.
The vote to determine Han's fate comes on the same day the Constitutional Court held its first hearing in a case reviewing whether to overturn the impeachment and reinstate Yoon or remove him permanently from office.
Speaking for the court in a preparatory hearing, Justice Cheong Hyung-sik said the court will move swiftly on the case considering its gravity, denying a request by Yoon's lawyers for a postponement in proceedings to better prepare the case.
The hearing follows weeks of defiance by Yoon ignoring requests by the court to submit documents as well as summons by investigators in a separate criminal case over his martial law declaration.
If Yoon is ousted, a new presidential election would be held within 60 days.
There has been overwhelming public support for Yoon's removal, according to opinion polls. (AP PHOTO)
Yoon shocked the country and the world with a late-night announcement on December 3 that he was imposing martial law to overcome political deadlock and root out "anti-state forces".
The military deployed special forces to the national assembly, the election commission, and the office of a liberal YouTube commentator.
It also issued orders banning activity by parliament and political parties, as well as calling for government control of the media.
But within hours 190 lawmakers had defied the cordons of troops and police and voted against Yoon's order. About six hours after his initial decree, Yoon rescinded the order.
Yoon and senior members of his administration also face criminal investigations for insurrection.
