A Singapore court on Monday sentenced four Chinese bus drivers to jail terms of up to seven weeks after they pleaded guilty to instigating the city-state's first strike in nearly three decades.

Liu Xiangying, 33, Gao Yue Qiang, 32 and Wang Xianjie, 39 -- all former drivers at state-linked Singapore transport firm SMRT -- were each sentenced to six weeks in prison for conspiring to launch a two-day strike last November.

He Jun Ling, 32, who faced an additional charge of provoking colleagues to stay away from work through an online posting, was jailed for seven weeks.

Another Chinese driver was sentenced to six weeks in jail in December while 29 others were deported without facing trial after the drivers staged a work stoppage to protest alleged pay discrimination and poor living conditions.

Judge See Kee Oon said after imposing the jail terms on Monday that "the sentence must be of sufficient duration to signal its deterrent intent" even though the strike "may have been motivated by a sense of grievance".

"This had the potential to severely affect the daily lives of all commuters who rely on public transport," the judge added.

The maximum punishment for staging an illegal strike in Singapore, which has tough laws against industrial unrest, is a jail term of up to a year as well as a Sg$2,000 ($1,640) fine.

The strike by the non-unionised Chinese drivers highlighted manpower-starved Singapore's heavy dependence on migrant labour to drive its economic growth.

Anyone convicted of a crime in Singapore can get a one-third reduction of his jail term for good behaviour but foreigners are normally deported immediately after serving their sentences.

Officials of SMRT admitted after the strike that the drivers had legitimate grievances, including bedbug-infested dormitories, but denied that the Chinese drivers were victims of pay discrimination.

Malaysian and Singapore drivers are paid higher by SMRT but are not hosted in dormitories.

Two of the drivers sentenced on Monday have accused Singapore police officers of assault while they were being held for questioning. Authorities have launched an inquiry into their accusations.

Singapore's last strike took place at a shipyard in 1986. Its strike-free environment has been a major attraction for multinational corporations.