An RCMP news release says police were called to a business in Nanaimo, north of Victoria, at around 7 a.m. after reports of shots fired.
Pat Kinney of the United Steelworkers union, which represents workers at the Western Forest Products mill, confirmed the shooting happened at the mill.
Police say one of the four people shot was airlifted to hospital, though none of the victims' conditions are known.
The news release says police arrived within minutes and apprehended a suspect.
The Mounties are expected to hold a news conference in Nanaimo soon.