Hong Kong immigration authorities have arrested 97 people in a joint operation with mainland China targeting an ID card forgery syndicate that was sending illegal workers into the city, with local agents disguising themselves as delivery men to apprehend the suspects.

Another 104 suspects were arrested on the continent, according to authorities.

So Chun-ho, a senior immigration official at the Immigration Department, said Thursday that local authorities and officers in Guangxi, Guangdong and Shenzhen made the arrests in July and August.

“The syndicate would attract people claiming to earn a lot of money in Hong Kong and provide ‘one-stop-shop’ services, such as the production of fake ID cards, accommodation and job guarantees, to encourage mainland residents to come and work in Hong Kong,” he said.

So border authorities first noticed the union in May, when its members created chat groups on mainland instant messaging apps seeking to recruit people willing to work illegally in Hong Kong. They each paid between 1,000 yuan ($140) and 2,000 yuan to buy fake ID cards before coming to the city.

The union would also deliver the cards to its city-based members using courier services to avoid detection. The members then handed over the documents to the illegal workers.

“On the day of the operation, our investigators disguised themselves as delivery men, simultaneously launching a controlled delivery to different locations in the city and arresting the recipients of the packages,” So explained.