A former SMRT station manager allegedly pilfered $20,000 in cash from Tanah Merah station, and is being investigated by the police.
The man is said to be on the run, and no longer in the country.
A police spokesman confirmed that the rail operator had lodged a report last Wednesday. He added that investigations are under way.
The Straits Times understands that the missing money - largely from commuters wanting to top up their travel cards at the station office - had been siphoned over a period of several months.
The case came to light apparently through an internal audit. Sources said the alleged culprit had worked at SMRT for only two years.
When contacted, SMRT spokesman Patrick Nathan said the company has referred the case to the police and that he could not comment further.
Each day, more than three million trips are made by close to one million people on Singapore's rail network. Observers estimate that if 3 per cent of the one million commuters topped up their travel cards by just $10 through the station office instead of the automated machines, the network would collect $300,000 in cash each day. And if the cash were to be evenly distributed, each station would be handling at least $3,000 a day, or $21,000 a week.
But according to insiders, busier stations could be handling much more than that.
Tanah Merah station, being an interchange where commuters go to and from Changi Airport, as well as Pasir Ris, Simei and Tampines, is one such busy station.
The Straits Times understands that by the time the missing money was discovered and the police report filed, the alleged perpetrator had already been away from Singapore for two months.
A source familiar with the work of a station manager said the handling of money is "based on trust".