Sun Hengchao, chairman of the privately owned Baota Petrochemical Group, was arrested on criminal charges after defaulting on debts, the financial unit of Baota Petrochemical said Monday in a statement.

Sun Peihua, chairman of the financial unit, who is Sun Hengchao’s son, was also arrested. It was unclear what violations the Suns are accused of. But several company sources said the charges are likely to be related to the company’s debt crisis.

As of the end of September, Baota Petrochemical had 34 billion yuan ($4.9 billion) of liabilities, including 26 billion yuan to be repaid within one year. The company’s actual debts could be even higher as it has used the financial unit for off-balance sheet borrowings, sources said.

Sun and the company have been listed as debt defaulters after repeatedly missing payments of 65 million yuan since July.

Related: Sun Hengchao: Private Sector Faces Difficulties in Financing