South Korean police raided Korean Air Lines headquarters in Seoul on Thursday as part of a probe into the youngest daughter of the airline's chairman, Yonhap News Agency said.
Cho Hyun-min, a senior vice president at the airline, is under investigation by police for possible assault after testimony that she "sprayed a drink towards them" during a business meeting.
Korean Air Lines shares fell as much as 4.1 percent while budget airline affiliate Jin Air, where Cho is an executive vice president, dropped 5.3 percent.
A Korean Air spokesman confirmed the raid, but did not elaborate on the reason. A police official declined to comment.
Cho, who is also known as Emily Cho, has apologized for her behavior, but says she "pushed" a cup of water and did not throw it at anyone's face as media have reported.
Her older sister Heather Cho made headlines over a notorious "nut rage" incident in 2014, when she lost her temper over the way she was served nuts in first class and ordered the Korean Air plane to return to its gate at a New York airport.
South Korea's customs agency is also looking into accusations that Cho and other family members did not pay customs duties on luxury goods brought into the country, the agency said on Wednesday.