The trouble at SMRT apparently started after its bus drivers from China received their payslips last Friday. It confirmed that they had not got any pay increase in the latest salary adjustment.
There were already murmurs of discontent last month, after SMRT put up a notice in the Woodlands dormitory that explained its latest salary increment.
That notice stated that foreign drivers would get a $50 increment - but this raise excluded Chinese nationals.
One of them, Mr He Jun Ling, 33, said that on Monday, a group gathered in front of the dorm to persuade other drivers to go on strike. The group that refused to work swelled to 171 in all, including him.
The Henan province native said drivers who did not turn up for work on Tuesday were not present at talks with SMRT management on Monday. He said they were unaware that SMRT had informed drivers it would decide on their salary requests in a week.
He said he did not go to work on Tuesday as he was sick.
Mr He said his compatriots had raised the issue of low pay with their supervisors and HR department several times, but had not received a proper response.
Since July, SMRT has required its drivers to work six days a week instead of five - a move that made drivers unhappy. It raised the pay of Chinese nationals by $75, Malaysian drivers by $150 and Singapore drivers by $425.
Last month, it raised the pay of Singapore drivers by $150 and Malaysian drivers by $50, but drivers from China got nothing.
An SMRT spokesman said SMRT had planned to review the pay of China drivers after October, and had approved a $25 increment last week.
This $25 increment was proposed to the drivers during Monday's talks, but they turned it down and asked for greater parity with Malaysian drivers.
Mr He, who has a daughter aged four back home, said the drivers had taken action as a last resort, and said he did not know they were breaking the law.
"We came here to work and earn money, not to create trouble," he said in Mandarin. "We are definitely worried about being sacked. But if we didn't fight for our rights now, we may stand to lose out more next time."
At 11pm last night, Chinese embassy officials turned up at the Woodlands dormitory and went inside to speak to the drivers.
