A South Korean regulator says Samsung Biologics Co. has breached accounting rules in a preliminary finding that could deal a big blow to the company and other Samsung affiliates if finalized.

Financial Supervisory Service said Wednesday it has wrapped up its one-year probe into Samsung Biologics and notified the company of the violation. It declined to confirm details of its interim conclusion pending a review at the Financial Services Commission. The notification gives Samsung Biologics a chance to defend itself.

Samsung Biologics is denying the accounting breaches.

Despite its defense, its stock price tanked, finishing 17.2 percent lower.

At stake is whether Samsung Biologics accurately evaluated the value of its affiliate Samsung Bioepis before its initial public offering in 2016.