Four Chinese bus drivers working with Singapore public transport operator SMRT have been arrested following a rare no-show over pay issues involving 171 Chinese bus drivers, the police said Thursday.

The four Chinese bus drivers were arrested between Wednesday and Thursday for their role in the "illegal strike" earlier this week, the police said.

Local media said the drivers will be charged in court on Thursday afternoon.

The Chinese Embassy said it was very concerned about the arrest of the Chinese citizens and was arranging consular visits to meet the Chinese bus drivers.

It also urged all the relevant parties to "be unbiased and clam and not to make things worse."

If found guilty of a role in an illegal strike, the drivers shall be liable to a fine not exceeding 2,000 Singapore dollars and an imprisonment of no more than 12 months.

The 171 Chinese drivers did not report to work on Monday over a recent pay rise that saw their fellow workers from Malaysia getting a larger increase. Some 88 of them continued to stay away from work on Tuesday. All the workers went back to work after Singapore authorities and the Chinese Embassy stepped in to urge the workers to resume their work.

Singapore's Acting Manpower Minister Tan Chuan-Jin described the incident as an "illegal strike." Some of the employees of SMRT, including 20 Chinese bus drivers, have been assisting the police in investigation into the incident.

Industrial disputes have been rare in Singapore over the past decades as authorities put in place measures that allows consultations involving both the workers, the employers and the government, while putting in place legal rules that make it virtually impossible to have a legal strike.

Under Singapore law, workers in essential services such as transport and public utilities must give their employer at least 14 days' advance notice of their intention to have a strike. The notice has to be signed by at least seven fellow workers involved in the strike or by at least seven union representatives of the workers. The notice then needs to be acknowledged and signed by the employer, after which, that notice needs to be put up in at least three conspicuous places where the workers are employed.