All Singaporeans passing through Woodlands Checkpoint by bus or on foot are now required to scan their thumbprints in a move to enhance security.
Until recently, only those opting for automated clearance were required to scan thumbprints using biometric technology.
But machines were recently added to staffed immigration lanes, so that Singaporeans must now give a thumbprint.
Vehicle lanes are not affected.
The Straits Times understands a similar system is in place at the Tuas Checkpoint, although a spokesman for the Immigration and Checkpoints Authority (ICA) declined to confirm this.
She did not comment either on whether the enhanced screening also affects permanent residents and foreigners.
The ICA said only that its BioScreen system, currently deployed at the automated lanes at the various checkpoints, is being progressively rolled out to the manned counters. The aim is to "facilitate the smooth immigration clearance of travellers while ensuring the continued high security of our borders against unauthorised and undesirable elements", added the spokesman.
The ICA did not say when the roll-out started, nor when the system will be extended to other checkpoints.
Currently, only travellers with biometric passports, which contain a computer chip embedded with the passport holder's thumbprint and unique facial features, can opt for automated clearance.
Machine-readable passports are being phased out.
When The Straits Times was at Woodlands recently, several travellers whose thumbprints could not be scanned, for whatever reasons, were taken to a separate office for further checks. Their thumbprints were re-scanned there.
Security experts noted that an increasing number of countries are turning to biometric technology that identifies a person by a unique human trait - say his fingerprints, the irises of his eyes, or even his voice - to step up security levels at checkpoints and other key installations.
The ICA has said before that the push for more travellers to use the automated system allows for more focused security checks on "unknown" travellers who are not Singapore citizens or registered card holders.
Assistant Professor Terence Fan of the Singapore Management University's Lee Kong Chian School of Business said the move towards biometric technology enhances border protection by matching the identity of the person holding the passport to the biometric details embedded within the document.
But travellers may be inconvenienced if the system does not accommodate people whose fingerprints may be hard to read.
He said: "I myself have sensitive skin which peels off easily and this sometimes gets me into 'trouble' if only thumbprint scanning is done. In some countries, all 10 fingers are scanned."
A traveller at Woodlands Checkpoint, who had to undergo further checks because her thumbprint could not be scanned, said: "I hope this does not happen each time I return from JB."