More SMRT employees, including "senior management", were disciplined for their role in the track accident on March 22 that killed two trainees.
In an internal mail message to staff on Wednesday, SMRT Trains managing director Lee Ling Wee said two employees had been dismissed and several others disciplined.
"Besides the two dismissals, verbal and written warning letters were issued to staff across several grades," Mr Lee wrote.
He also alluded to pay cuts and, possibly, demotions.
"Individual performance grades were recalibrated downwards across various levels of the Trains team, including senior management," he said.
Mr Lee's communication came swiftly after The Straits Times reported on Wednesday that two SMRT employees had been sacked over the fatal accident, including the driver of the train that hit the two trainees.
On the morning of March 22, Mr Nasrulhudin Najumudin, 26, and Mr Muhammad Asyraf Ahmad Buhari, 24, were among 15 men on the track near the Pasir Ris station when they were hit by an oncoming train.
The Straits Times understands that the driver might not have seen the workmen on the track and, if he had seen them, did not sound the horn as required. According to sources, the train had switched tracks moments before hitting the workers. Train drivers have no control over track switching.
A second employee, said to be part of the work team on the track that day, was also dismissed.
The Straits Times understands that a senior controller of the network's Operations Control Centre also left following the accident.
In his mail message to staff, Mr Lee said: "Our disciplinary process is fair. We do not single out any staff or department to bear the responsibility when things go wrong."
He said there had been previous dismissals for safety breaches.
"We did this in an all-out effort to never again repeat safety lapses," he wrote.
Since the tragedy - the second fatal track incident in six years involving employees - SMRT has set up a Track Access Management Office "to control access to railway tracks".
Mr Lee also said any staff member, regardless of rank, can "call a time-out if they feel safety is compromised".
SMRT said in April that failure to follow safety measures had led to the accident.
There were several lapses, including allowing a train to ply in automatic mode while workers were on site, not deploying watchmen to look out for approaching trains, and failing to provide early warning to the work team.