Police dropped assault charges against Cho and referred her only on the charge of obstruction of business as the victims did not seek punishment. Under local law, assault charges can only be brought against a suspect when the victim wants the assailant to be held accountable.

Police sought an arrest warrant for Cho early this month, but state prosecutors turned it down citing a lack of grounds for charging her.

Hyun-min is the younger sister of Cho Hyun-ah, who gained global notoriety for the "nut rage" incident in 2014. She forced a plane back to the boarding gate at New York's John F. Kennedy International Airport because she was upset with the way her nuts were served -- in an unopened bag instead of on a plate.

In March, Hyun-ah made a comeback as the head of KAL Hotel Network, the operator of the Grand Hyatt Incheon near Incheon International Airport.

Both sisters have since been stripped of their company posts.

Meanwhile, the chief of the country's customs office said Korean Air Lines Chairman Cho Yang-ho and his only son Won-tae, president of Korean Air Lines, will be questioned over allegations of smuggling.

Earlier, the customs office said Hyun-min, her older sister Hyun-ah and their mother are on the list for questioning.

The Korea Customs Service has been investigating allegations that the founding family members have smuggled luxury goods into the country without properly paying duties.

The customs office carried out three rounds of searches of the airline's headquarters and the family members' house over the suspicions raised by some former and current employees that the chairman's children and even his wife circumvented the law using the company to bring in goods from overseas without proper declaration.

Smuggling is an offense that carries a maximum sentence of five years in prison and fines up to 10 times the duties evaded.

"We have to call in (Chairman Cho and his son) if there is a need to do so," Kim Young-moo, the chief of the KCS, said in a radio interview. (Yonhap)