The state antitrust regulator has fined SK Group Chairman Chey Tae-won amid allegations that he illegally earned large profits from the group's 2017 purchase of a silicon wafer manufacturer.

The Fair Trade Commission(FTC) on Wednesday slapped an 800-million-won fine on Chey and another on SK Holdings, the group's holding firm. It also ordered corrective action. 

The FTC, however, decided not to file a complaint with the prosecution.

The Solidarity for Economic Reform and others had filed for an FTC investigation into allegations that SK Holdings purchased 70-point-six percent of LG Siltron, LG Group's wafer producer, in 2017, leaving the rest for Chey.

Chey acquired the remaining 29-point-four-percent stake at a lower cost from creditor banks, allowing SK Holdings and Chey to wholly own the company.

The FTC ruled that SK Holdings scrapped initial plans to purchase the remaining stake, after Chey expressed his wish to buy them himself. The holding firm also supported Chey in the takeover.

Under the fair trade law, large business groups with assets exceeding five trillion won are prohibited from giving undue profits to their chiefs through lucrative business opportunities.