SINGAPORE (AP) — Four Chinese immigrant workers who organized Singapore's first strike in nearly three decades were charged Thursday with instigating labor unrest.

The men who worked as bus drivers for the island's public transport company are in jail while an investigation continues and face up to a year in prison if found guilty.

Strikes are almost unheard of in Singapore where the ruling party has been in power since 1959 and maintains strict control over political dissent. The last strike was in 1986 by shipyard workers.

Some 171 Chinese bus drivers went on strike Monday in protest at being paid nearly a quarter less than Malaysian bus drivers who work for the same Singapore transport company. The strike, which disrupted about 5 percent of the city-state's bus services, was over by Wednesday.

Singapore law requires essential service workers such as bus drivers to give 14 days notice of a strike.

China's embassy in Singapore sent an official to the court hearing as an observer. She declined to comment on the case.

One of the men, He Jun Liang, faces an additional charge of posing material online that urged other bus drivers to strike.

Singapore relies on hundreds of thousands of immigrants from countries such as Indonesia, Bangladesh and China to work as maids, construction workers and other jobs deemed unappealing by many locals.