More than 100 SMRT bus drivers refused to go to work early Monday morning and instead assembled at their dormitory in Woodlands.

The drivers, who are Chinese nationals, were unhappy about the recent pay increase that Malaysian drivers had received, reported Chinese newspaper Shin Min Daily News.

Malaysian drivers got a $275 increment and a month's bonus, while Chinese nationals were paid $75 extra without any bonus.

An SMRT human resource executive was called in to resolve the dispute but when the discussion came to a standstill, police with their riot vans were called.

SMRT runs about 25 per cent of Singapore's bus routes with SBS Transit running the rest.