Singapore's first strike in 26 years ended on Wednesday when mainland Chinese bus drivers demanding higher pay reported for duty after two days of protest that angered the city-state's government.
State-linked transport operator SMRT said the rate of attendance of its bus drivers on Wednesday was "back to normal and all our bus services are running as scheduled".
It said 20 of the drivers were "assisting the police" in an investigation after their action was declared illegal by the manpower ministry, which warned that anyone found guilty could be fined or jailed for up to a year.
The Chinese drivers, who are not unionised and issued no strike declaration, told reporters on Monday that they were protesting pay discrimination because their Malaysian counterparts were getting higher wages for the same work.
The company, which must hire foreigners due to a chronic labour shortage in Singapore, said 171 Chinese drivers took part in the work stoppage on Monday, and 88 stayed off work on Tuesday.
SMRT said it pays "competitive wages" and provides housing, utilities and worksite shuttles to its Chinese drivers.
But it vowed to look into the grievances of the strikers and address problems like bedbugs in dormitories.
Most Malaysian blue-collar workers in Singapore commute daily across a causeway linking the two countries.
"There are lessons from this episode, including how we can better engage our (drivers), and we will improve in this area," said Teo Chew Hoon, an executive vice president of SMRT.
"In the meantime, we are doing our utmost to make immediate improvements to their living conditions," she added.
Strikes and other forms of industrial action are extremely rare in Singapore, where unions work closely with the government and private business, making the port city an attractive place for foreign investment.
The last strike in Singapore was staged in 1986, the manpower ministry said.
Strikes are illegal for workers in "essential services" such as transport unless they give a 14-day notice of their intent and comply with other requirements.
The penalty for an illegal strike is a fine of up to Sg$2,000 ($1,636) or a maximum prison term of one year, or both.
The wildcat strike began when the Chinese drivers refused to board a shuttle bus from their dormitory to a nearby depot on Monday. Local media reported that some of the drivers were apparently unaware they were breaking Singapore law.
Police had no immediate comment on the investigations.
SMRT is 54 per cent owned by state investment firm Temasek Holdings.