They hire their Uber through the app just like any other passenger, and hop in the back of the car.
But halfway through the ride, the mood changes and they reveal their identity.
"Pull over here. It's you. You are in trouble for driving an Uber," the passenger tells his driver, during one of a few recent encounters captured on video and circulated online in Hong Kong.
The passengers aren't traffic cops. They are vigilante taxi drivers taking direct action, having become increasingly frustrated about Hong Kong authorities' failure to regulate the ride-hailing platform.
After the car pulls over, they hand over the driver, often still reeling in shock, to the police officers they have called.
"You may say this is provocative. But without these videos, people may think we inflate the numbers of 'white-plate vehicles' out there," one of the taxi drivers who took part in a sting operation, and asked to be only identified as Ka Chun, told CNN.
"White-plate vehicles" is how taxi drivers colloquially refer to Uber. "We just want the government to enforce the law," Ka Chun said.
Uber remains technically illegal in Hong Kong, which it entered in 2014. But it has thrived under the ambiguous approach of officials keen to project an image of technological modernity.
"Uber is often framed as innovation, which seems to contribute to the 'smart city' vision – something that the Hong Kong government has strived to be," said Oliver Chan, an assistant communications studies professor who specializes in the gig economy at Chinese University of Hong Kong (CUHK).
Ads for the US-headquartered company are widespread, and its drivers are highly unlikely to face problems with the authorities.
Taxi drivers have for years complained about how Uber has flouted local laws, upended the market, and chipped away their already modest earnings.
But their recent acts of vigilantism appear to have backfired.
Instead of rallying public support, the cabbies were on the receiving end of a backlash, with passengers taking to social media to share their bad experiences of rude taxi drivers, ride rejections and opportunistic charging during heavy rains and the city's regular summer typhoons.
"They charge arbitrarily and refuse to take passengers. And yet, they have the audacity to go on sting operations," one person wrote on LIHKG, a popular local internet forum, adding: "Shameless people know no bounds."
Others have retaliated by reporting law-breaking taxi drivers to police.
Pictures of taxis parking in restricted areas flooded the internet in posts calling for people to report them. WhatsApp groups set up by Uber drivers also discuss how to retaliate, one driver told CNN.
So tense is the backlash that Hong Kong leader John Lee, when asked about the furor by reporters last week, acknowledged the "fierce public debate" and appealed for calm. He urged taxi drivers to stay away from any vigilante acts.
Cities around the world have grappled with how to regulate Uber since its launch more than a decade ago. Tensions in Hong Kong have risen as the city struggles to lure back tourists after years of economic struggle due to the Covid-19 pandemic.
Hong Kong's government is expected to unveil a study on online ride-hailing services in July. A spokesman said it is "open-minded" on the apps, though "they must be in compliance with the relevant law and regulations."
Keep reading about the city's Uber spat here.
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