The Land Transport Department apprehended and fined 18 drivers of Uber cars on Monday as it continued its blitz on the popular but illegal taxi service.
Director-general Sanit Promwong said department officials were assisted by police and soldiers in the operation.
Eighteen Uber drivers were stopped and each fined 2,000 baht for using their vehicles as public transport without authorisation, and another 2,000 baht for wrongful use of the cars.
Their names and offences had been put into the department's data base and their driving licences could be revoked if they continue to take passengers, he said.
The drivers will be required to undergo a three-hour training course on attitude and legal matters, according to Mr Sanit.
The operation on Monday was the largest yet against Uber and other operators of ride-hailing companies, including Grab.
Transport officials began their campaign in Chiang Mai last week, cracking down on Uber and Grab services.
Cars registered as private vehicles are not allowed to provide public transport services, such as provided via internet apps by ride-sharing companies.
The department has netted 83 drivers since December 2014 when it banned the two firms from operating in Thailand, Sukree Jaruphoum, who is in charge of public service inspection at the department, told TV 3 on Friday.
"They are definitely against the law because their cars are registered for private use only," Nanthapong Cherdchu, the department deputy director-general, said in an interview with the station.
Despite the official crackdown, Uber expanded its service to Chon Buri municipality and Bang Saen area in the same province last Thursday, after setting foot in Pattaya in February, according to the Uber Facebook page.
Uber told customers on its Facebook on Sunday that the firm will continue talks with authorities to ensure people continue to benefit from ride-sharing.