The factories all belong to Phuoc Tan Industrial Park (IP) in Bien Hoa Town of Dong Nai that borders Ho Chi Minh City.
The violation was uncovered following two years of comprehensive IP inspection, provincial authorities stated Wednesday.
The 72 ha of forest land in Phuoc Tan Ward of Bien Hoa Town have yet to be designated as land for commercial and service purposes, though a series of companies had erected 45 factories and workshops here starting 2010.
Of the facilities, four had illegally adjusted their land use purposes, while the rest had ignored legal procedures in their entirety.
Inspectors also reported 34 violations of environmental law, 22 illegal electricity usage and 37 breaches of fire safety.
The provincial People's Committee holds authorities of Bien Hoa Town and Phuoc Tan Ward, as well as authorities of Long Thanh District, the former state of Bien Hoa, responsible for the illegal activity.
Further investigations are undergoing.