Police began a formal probe Friday into the allegations that the wife of Hanjin Group Chairman Cho Yang-ho bullied workers several years ago.
Lee Myung-hee, 69, is accused of assaulting or abusing several workers at a hotel construction site in 2014.
Police launched the investigation into the case after unofficially collecting related information for about two weeks.
Investigators plan to summon Lee for questioning.
Her scandal-ridden family, who controls the Hanjin conglomerate with many affiliates, including Korean Air, has come under public criticism following reports that Lee's daughter, Cho Hyun-min, recently physically abused two employees at an advertising firm with a contract with Korean Air. The incident occurred while Cho was serving as director at the airline. She later stepped down from the post.
Police sought to arrest Cho but prosecutors refused to seek an arrest warrant, saying the victims do not want her to be punished legally and a further probe is needed to determine if she's guilty or not.
Upset about the family's routine abuse of their power, some pilots and other Korean Air employees, all wearing face masks, held a rally in Seoul on Friday. They demanded the Cho family quit the company.