Walmart Canada is investigating after two security guards restrained a woman who claimed to be pregnant outside an Edmonton store Sunday night — and witnesses say the men used excessive force.

The woman, who remains unidentified, was taken to hospital and treated for "non-life-threatening injuries" and later charged with theft under $5,000.

The incident began at about 9 p.m. when the woman left the Walmart store at Stony Plain Road and 184th Street.

She was followed outside by loss prevention officers. After a struggle, the two men pushed the woman face down in the parking lot.

Each guard held one of the woman's arms behind her back. Both knelt on her back. On a video recorded by a witness, the woman could be heard screaming "I can't breathe."

One guard replied, "If you can talk, you can breathe."

The same guard was then heard talking with a bystander who questioned his use of force.

"Then call 911 and charge me," he told the bystander.

As the two continued to hold the woman down, she screamed, "Just roll me on my stomach, please."

"No," the guard replied.

Shortly after that, the woman told the guard she was pregnant.

Another 45 seconds passed before the woman was allowed to get up. She was then taken into the store by the two guards.

In all, the woman was held down for more than three minutes.

Woman taken to hospital

Edmonton police spokesperson Carolin Maran said officers responded to a shoplifting report from the area on Sunday at about 9:30 p.m.

"Upon arrival, officers found a 28-year-old female in the custody of loss prevention officers," Maran wrote in an emailed statement.

Two security guards wrestled a woman to the ground outside a Walmart in West Edmonton on Sunday. (Brynne Agar)

"It was reported that the female was allegedly shoplifting and resisted arrest by the loss prevention officers."

The woman was taken to hospital with "non-life threatening injuries" and was later released on a promise to appear in court.

She has been charged with theft under $5,000, and also faces charges related to three outstanding warrants.

Loss prevention officers, who are not required to wear uniforms, are licensed by the province to work as security staff for commercial, industrial or retail properties.

Brynn Agar said she was in the parking lot Sunday and began recording the encounter after she saw what was happening.

"I saw them using too much force," she said. "I saw one woman, a very small woman, against two larger men. And I thought, I want to stay here and tell the police what I saw. You know, she has rights just as much as they have rights."

"I think it was excessive. I think it was an abuse of power."

Agar said she arranged to make a statement to police Monday night.

"Everyone's innocent until proven guilty," she said. "It's not like she had a weapon on her. She wasn't attacking anybody."

"These men put their hands on her first ," she said. "If you were walking out of a store and, from behind you, two men grabbed you, would you not fight back?"

"For all she knows, she could have been being attacked or kidnapped or something."

Walmart responds

In a three-sentence email to CBC News, a Walmart Canada spokesperson said the corporation is aware of the incident.

"We can confirm that we are looking into the situation and will take appropriate action as necessary."

Three years ago, a violent takedown of a shoplifter at the same Walmart prompted questions about security staff training.

A video of the 2014 incident shows two loss prevention officers wrestling with a man believed to be a shoplifter.

The man stabbed one of the officers during the scuffle.