The South Korea prosecutor’s office reportedly plans to summons Kia Motors Corp. CEO Chung Eui-sun this week for questioning regarding a Hyundai Motor Group bribery probe.

Authorities are investigating whether some Hyundai Motor Group-affiliated companies used millions of dollars in slush funds to illegally lobby public officials regarding various merger and construction programs.

They also are said to be looking into how the Chung family-owned conglomerates shift money within group companies to maintain control of their businesses.

Prosecutors earlier in the week detained Hyundai Motor Co. Ltd. Vice President Kim Dong-jin for questioning. Kim is responsible for the auto maker’s financial operations.

Hyundai Motor Group Chairman Chung Mong-koo on Wednesday (April 19) apologized for causing “concern” to South Korean society over the probe and said he and his son, Kia’s Chung Eui-sun, would donate $1 billion of their company shares in logistics affiliate Glovis Co. to charity.

The Chungs, together, control a 60% share of Glovis.

“Hyundai will cooperate actively with the prosecutors’ investigation and humbly accept the outcome of the probe,” the company says in a statement.

Hyundai investors hope the donation will help ease pressure from the investigation, Reuters says in a report.