The SMRT bus drivers from China, who refused to report for duty earlier this week over a wage dispute, returned to work on Wednesday.
They were seen boarding buses, which would ferry them to the various bus depots, from their dormitories at both Woodlands and Serangoon Gardens at 3.45am and 4am.
Two police officers were spotted at Serangoon Gardens, monitoring the situation. They left after speaking briefly with the driver of the 4am bus.
Before boarding the buses, each driver was also given a notice written in Chinese by a supervisor.
The Straits Times understands the notice contained information regarding the incident that transpired over the last two days.
The Government on Tuesday said it plans to take action against the bus drivers from China who refused to turn up for work because they were unhappy with their wages.
It also described what they did as an "illegal strike", and said the bus drivers would be dealt with if found guilty.
Meanwhile, it has put in place contingency plans to shore up bus services in case the strike is prolonged.
Describing the drivers' action as unacceptable because it disrupts an essential service, Acting Manpower Minister Tan Chuan-Jin said during a press conference on Tuesday that the police are investigating.
SMRT said that on Monday, 171 drivers staged a sit-in the workers' dormitory in Woodlands.
On Tuesday, 88 remained defiant by refusing to return to work. They are protesting against what they deem to be inequitable pay and poor living conditions.