Italian-Thai Development Plc president Premchai Karnasuta will face an additional charge of "conspiracy of two persons and above to offer a bribe to state officials" along with his driver Yong Dotekreau, Counter-Corruption Division (CCD) chief Pol Maj-General Kamol Rianracha said on Thursday.
The two men are scheduled to hear the new charge on Monday.
Yong is accused of asking officials to release Premchai after his arrest on suspicion of poaching and offering to give them equipment.
The new charge stems from the CCD’s interview on Wednesday with sanctuary chief Wichian Shinwong about the alleged bribery attempt.
Premchai, Yong and two others, Natee Riemsaen and Thanee Thummart, face more than nine charges including poaching, possession of weapons without permits and possession of the remains of protected animals following their arrest at a forest campsite in early February in Kanchanaburi's Thung Yai Naresuan Wildlife Sanctuary.