In the past two months, three major sting operations on Hells Angels motorcycle gang facilities and marijuana growers has resulted in some 370 new inmates for the province's 18 prisons, The Gazette newspaper in Montreal reported.
Stephane Lemaire, head of the union of Quebec correctional officers, told the newspaper the raids made an existing problem worse.
"Our system has been overcrowded for two, three years," he said.
Eric Belisle, a spokesman for an inmates rights group, agreed, and claimed provincial prisons were already 116 percent full before the most recent string of raids.
The provincial government has provided trailer facilities at existing prisons that can hold 300 prisoners, but only those considered low-risk, the report said.
Lemaire told The Gazette that in some facilities as many as 50 inmates are sleeping on mattresses on the floor of common rooms, while others were being shuttled as far as 360 miles away to be accommodated.