The Canadian Civil Liberties Association issued the call along with the National Union of Public and General Employees after hearing witness accounts during hearings in November.
"Peaceful protesters, journalists, innocent bystanders and others told horrific stories of police violence, threats, mistreatment and unlawful detainment," the group said.
"During the hearings we heard shocking stories of police excesses at the G20 Summit," said union President James Clancy. "In many cases, it seems as if these excesses ... were committed with complete impunity."
"It is imperative that there be a full public inquiry," said CCLA counsel Nathalie Des Rosiers.
More than 1,105 people were arrested during the protest against the global economic summit, the largest mass arrest in Canada's peacetime history.
The groups also want the absence of police while vandalism was committed, the absence of fire crews when police cars were burned and lack of medical aid for the injured investigated.
The parliamentary public safety spokesmen of the opposition Liberal and New Democratic parties supported the demand for a probe.
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