Shares of marketing firm Artist United — which counts actors Lee Jung Jae and Jung Woo Sung as co-owners — dropped more than 20% on Thursday after insider trading allegations were raised against the company.

By 11:11 a.m. local time, the stock plummeted to 13,270 KRW ($9.34), which is 21.62% lower from the previous day. Within the time frame, it reached a bottom of 11,860 KRW ($8.35).

That major sell-off was reportedly triggered by media coverage of South Korean financial regulators looking into suspected insider trading on Artist United, formerly Widerplanet.

It is being reported that a small fraction of people may have tried to game the stock market by branding Artist United, and political stock can be manipulated to drive its price up so the seller can make a healthy profit.

AllKpop reported that Artist United has issued a statement clarifying that Lee Jung Jae has not done anything wrong and that he is just a witness.

The company further explained that neither Lee nor his management agency, Artist Company, was involved in any illegal action concerning insider trading or any leakage of information at the time of the capital increase last year.

"While it's true that the former Widerplanet (now Artist United) is under investigation by financial authorities, Lee Jung Jae and Artist Company are not subjects of the probe. We will actively cooperate to clear any misunderstandings."

The firm promised to take legal action against everyone involved in possible insider trading or leak of information.

Investors began to suspect the company when Widerplanet announced capital increases in December 2023 and the stock price and trading volume surged.

Artist United vows to "conduct its own investigation and closely hold accountable anyone who is found to be involved in misconduct — we have a duty to protect our shareholders from undue losses."