Investigators said the group used devices designed to interfere with the monitoring system installed in electric taxis operated by GSM, the company behind the Xanh SM taxi service.
The infrared-based system installed in VinFast electric taxis detects passengers in front and rear seats. Police said signal-jamming devices prevented the system from registering riders, allowing drivers to conceal trips and divert fares from the company.
The scheme first came to light after police monitoring and online investigations uncovered the sale of devices capable of disabling taxi monitoring systems in Thai Nguyen from late 2025.
In late April, GSM reported that several drivers had illegally tampered with vehicle sensors to manipulate fare records.
Police later caught three GSM drivers transporting passengers while using the devices during an inspection in Phu Binh Commune on April 28.
The three men were identified as Trinh Ngoc Chien, 34, Dinh Quy Duong, 30, and Nguyen Trung Thanh, 36.
Investigators later summoned a fourth suspect, Ma Khanh Hung, 26, accused of supplying the devices to drivers.
Police seized eight electronic devices allegedly used to interfere with the passenger-recognition system, along with related documents and evidence.
According to investigators, Hung had previously worked as a GSM driver before being dismissed after allegedly using the device himself. Police said he later began selling the equipment to other drivers for between VND 500,000 and USD 900,000 (USD 19-USD 34) each.
Authorities said the drivers repeatedly used the devices to hide passenger trips and misappropriate taxi fares from GSM.
The four suspects were formally charged and placed in pre-trial detention on April 30 on allegations of using computer and telecommunications networks and electronic means to appropriate property.
The investigation is ongoing.