The walkout this week by the drivers from China, over pay disparities and conditions at their dormitory, was the first major strike in tightly regulated Singapore in more than 25 years. It was mostly over by Wednesday.

Singapore, an ethnic Chinese-majority island with no minimum wage, prohibits workers in public transport and other essential services from taking industrial action without giving notice 14 days in advance.

The four men from China men were arrested on Wednesday and Thursday for the offence of instigating or inciting an illegal strike, the police said in a statement.

They were formally charged on Thursday, media reported, saying court documents showed the alleged ringleader incited his colleagues in an online message titled "The insults and humiliation suffered by Singapore drivers".

If convicted, the men face a maximum fine of S$2,000 and/or a sentence of up to a year in prison.

In a statement, China's Commerce Ministry said it is "paying very close attention to this labour dispute".

It said it "hopes related parties will properly handle and respond positively to the reasonable demands of Chinese drivers to be paid the same wages for doing the same work and be treated fairly, and protect the legal rights of Chinese workers."

Strikes of any kind are rare in the city-state, where the long-ruling government keeps a tight lid on labour unrest that might deter investors. At the same time, it must contend with a shortage of lower-skilled labour and address the anger of many Singaporeans about the number of immigrants.

Acting Manpower Minister Tan Chuan Jin said this week he expected bus, train and taxi operator SMRT Corp Ltd (SMRT.SI), controlled by state investor Temasek Holdings Pte Ltd , to address the grievances but that there was "zero tolerance for such unlawful action" by the Chinese drivers.

(Additional reporting by Hui Li in BEIJING; Editing by Robert Birsel)

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