The tainted formula gave babies painful kidney stones and news of the problem sent parents around the country rushing their babies to emergency rooms for tests to see if they were affected. Chinese dairy exports such as chocolate and yogurt were also found to be tainted, triggering a slew of product recalls elsewhere in Asia and in Europe, Africa and Latin America.

At least four of the suspects on trial Monday could be given the death penalty.

Hearings were held in the northern city of Shijiazhuang, where the company at the heart of the scandal — Sanlu Group Co. — is headquartered, along with three other cities in surrounding Hebei province, according to state broadcaster CCTV and the Xinhua News Agency.

The first trials in the case began for six men on Friday.

All 15 on trial have been charged with producing and selling melamine. The industrial chemical was added to raw milk because — like protein — it is high in nitrogen and can make protein levels appear higher.

Sanlu's chairwoman and general manager, Tian Wenhua, is scheduled to go before a Shijiazhuang court Wednesday.