On Monday, all six current justices of the court will attend the first meeting over the impeachment, which the opposition-led parliament passed on Saturday.
The court has up to six months to decide whether to remove Yoon from office or to reinstate him.
Yoon and a number of senior officials face potential charges of insurrection, for the short-lived martial law.
Investigators plan to question South Korean President Yoon Suk Yeol over his martial law decision. (AP PHOTO)
A joint team of investigators from the police, the defence ministry and an anti-corruption agency are planning to call Yoon in for questioning on Wednesday, Yonhap news reported.
The investigators' office could not be immediately reached for confirmation.
On Sunday, Yoon did not appear in response to a summons for questioning by a separate investigation by the prosecutors' office, Yonhap news reported.
His presidential powers will be suspended until the Constitutional Court decides whether to formally remove him from office or reinstate him.
The court has up to 180 days to rule. But observers say that a court ruling could come faster.
In the case of parliamentary impeachments of past presidents - Roh Moo-hyun in 2004 and Park Geun-hye in 2016 - the court spent 63 days and 91 days respectively before determining to reinstate Roh and dismiss Park.
- with AP
