Special Investigations Unit spokeswoman Monica Hudon said three Peel region police officers approached the woman around 3:30 a.m. last Wednesday as she was walking along a road in Mississauga.
Hudon said officers spoke with the woman until "at some point" in the incident an officer fired his Taser.
Hudon said the elderly woman fell to the ground and was rushed to Credit Valley Hospital for treatment of a fractured hip, among other injuries.
The SIU is an arm's length agency that investigates reports involving police where there has been death, serious injury or allegations of sexual assault.
The incident occurred one day after the province announced it would permit all front-line police officers to carry stun guns.
The use of force by police in Ontario has come under scrutiny after Sammy Yatim, 18, was shot multiple times and Tasered by police during a confrontation on an empty streetcar.
Videos of the incident prompted hundreds of people to take to the streets to demand justice.
Another high profile case that brought the police use of Taser under public scrutiny was the 2007 death of a Polish immigrant at Vancouver's airport.
Robert Dziekanski died after being stunned with a Taser by RCMP officers. A public inquiry found that the officers were not justified in using the Taser.
The move by the Ontario government to permit all front-line officers to use the stun gun means it's now up to local police services in the province to decide whether they want to equip all their officers with Tasers, which are currently restricted to supervisors and specialists, such as tactical units and hostage rescue teams.
Police forces will also have to foot the bill if they want to arm their officers with Tasers — costing about $1,500 each — which will put pressure on municipal budgets.
Ontario police chiefs and associations have been pushing the government for years to expand the use of stun guns, to no avail. Coroner's inquests have also recommended expanding the use of stun guns since 2004.
Many police forces, including the Ontario Provincial Police and Toronto Police Services, have said they plan to train and equip their officers with stun guns, in addition to the sidearm, extendable baton and pepper spray that they currently carry.
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