Looking to earn some extra money, Chinese national Chen Jie, 35, used his employer's van to deliver duty-unpaid cigarettes.
He had been hired by fellow Chinese national Zheng Chao Lin, 23.
When they were caught, more than 1,873 cartons of illegal cigarettes and the company van were seized.
The duty and GST evaded amounted to about $145,380 and $14,630 respectively.
Chen and Zheng were each sentenced to four months' jail, and slapped with fines of $1,250 and $1,000 respectively in November.
The duo were among 21 foreign workers on work permits caught last year, for their involvement in duty-unpaid cigarette activities, said a media release from the Singapore Customs yesterday.
In response to queries from The Straits Times, a spokesman said it started monitoring the trend in mid-2015, when nine workers were caught.
According to the Singapore Customs, the workers usually solicit for jobs on social media platforms, such as QQ and Shi Cheng BBS, and chat apps such as WeChat.
They are hired by syndicates to deliver duty-unpaid cigarettes.
The Customs statement also highlighted two similar cases last year, in which Chinese nationals were caught.
They were recruited after posting advertisements online seeking work.
The Customs' spokesman said it also engages workers and employers to raise awareness on the consequences of dealing with illegal cigarettes.
During its outreach sessions to companies, it advises employers who allow their workers to drive company vehicles outside working hours to closely monitor their use.
The spokesman said: "This will help to prevent the company vehicles from being misused for illegal activities and help the vehicle owners avoid any inconvenience and financial loss."
Employers told The Straits Times that foreign workers moonlighting and turning to illicit activities to make a quick buck has been happening over the years.
Mr Hooi Yu Koh, 46, chief executive and managing director of engineering company Kori Holdings, said: "It's profitable, for sure. As compared with a proper job, these activities pay you instantly in cash. Workers do get tempted ."
Fortunately, the company, which hires about 300 workers from countries such as Bangladesh and China, has not experienced such a case, added Mr Hooi.
A spokesman for construction and engineering company Koh Brothers Group said while it has not seen this among the 1,000 foreign workers it hires, there are stringent measures to ensure that they understand Singapore laws and the terms of their work permits.
Besides regular briefings by security and dormitory managers and police officers, Koh Brothers appoints 15 of the workers to look out for fellow employees.
The spokesman said: "We take this very seriously and will come down hard on those who engage in illegal activities. They know that it can result in termination of their work permitand they will also face repatriation."
This article was first published on Jan 13, 2017.
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