The Public Service Division (PSD) has said that civil servants need to declare additional trade or work that draws income to ensure that there is no conflict of interest.
Civil servants can apply for permission and the request will be considered on a case-by-case basis, a spokesman told The Straits Times. The Singapore public service is the largest employer here, with about 145,000 officers.
The statement follows news last week that the SAF had fined a staff sergeant $2,000 for giving 140 rides using the GrabHitch app between October and March. The SAF regular had not sought prior approval. The case was detailed in a screenshot posted on social media, showing an SAF case study of moonlighting.
With GrabHitch, private car owners are paid a distance-based fare. Grab says the service "encourages road users to carpool... and contribute to a car-lite movement".
The Road Traffic Act permits car owners to offer at most two paid carpooling trips a day. While human resources experts say employers have good reason to view paid carpooling as moonlighting, Grab disagrees. It says drivers do not make a profit from the service.
Mr F. Shahrukh Riza, 24, a car-rental business owner who ferries people using GrabHitch about twice a week and has been using the app for more than two years, said: "It isn't going to make you any richer; it's just going to cover your expenses at the end of the day."
The maximum amount a passenger pays for a trip is about $15, which Mr Shahrukh said on average just covers costs. These include petrol, parking and maintenance.
"And it (carpooling) won't affect your work, unless you are late for work because of it," he added.
However, Ms Linda Teo, country manager of human resources consultancy ManpowerGroup Singapore, said employers see it as moonlighting, since the driver receives payment for a service rendered.
But she added: "These days, more people are moonlighting to supplement their income due to the rising cost of living. Most employers do not explicitly state that moonlighting is not allowed in their employment contracts, so they adopt a 'don't-ask-don't-tell' approach."
She said when formulating a policy on moonlighting, employers should consider whether the policy is fair to the employees and clearly state what is permissible.
Mr Erman Tan, president of the Singapore Human Resources Institute, said the public sector has stringent policies. "It has to ensure that there is no conflict of interest or corruption, since their public duty cannot be compromised," he said.
But in the private sector, corporate culture and attitudes towards moonlighting will run the whole range, said Mr Tan. "Large companies like multinational corporations will typically have stricter policies, while smaller ones... tend to be more lenient as they may not pay their staff as well as large corporations."
Mr Tan reckons that it is up to individual firms and their employees to make the judgment call. "Singapore has a high degree of professionalism and work ethics, and people know what is right or wrong."
Correction note: This story has been edited for clarity.