
The sting comes as the San Francisco giant has encountered regulatory roadblocks around the world, despite its huge popularity, and after five Uber drivers in the southern Chinese city were found guilty of operating without proper licences in March.
Those drivers were arrested in a dramatic police swoop in 2015 after furious traditional cabbies smashed up their own taxis with hammers and called for authorities to act over unlicensed cars.
Uber ordered to return stolen Waymo files
"Police took action today ... arresting 21 drivers, including 20 males and one female," police spokesperson Edwin Lau told reporters.
"We sent decoys on many trips, eventually we took all the evidence," Lau said, describing the undercover operation that took place earlier this month.
The drivers were arrested for illegally carrying passengers for reward and for not having third party insurance, he added.
Uber is the most prominent of several smartphone apps that are shaking up the traditional taxi landscape in cities around the world.
But it has faced criticism and significant resistance from regulators in several countries, who accuse it of unfair competition and a lack of standards.
Uber extends sexual harassment probe; expects report by end-May
Uber was not immediately available for comment when contacted by AFP.
In April, Uber said it would relaunch its services in Taiwan with a new business model following a two-month hiatus on the island after sparring with authorities over legal issues.
In January, Taiwanese authorities hiked the maximum possible penalty to Tw$25 million ($816,000) per driver -- the highest in the world.
The company withdrew from the market a month later, criticising the government's actions for hindering innovation and calling on President Tsai Ing-wen to take action.
It was also in April fined for operating an illegal taxi service in South Korea, where the service sparked angry protests from taxi drivers.
COMMENTS
Comments are moderated and generally will be posted if they are on-topic and not abusive.
For more information, please see our Comments FAQ