Carla Cheney, who worked as a pharmacy technician, told CBC News she hadn't started working and sitting in her own clothes at a table with colleagues outside the Wal-Mart in Kemptville, Ont., on Tuesday when she spotted a customer leaving his dog in a parked truck.
She said she confronted him later when he drove up to her table on the way out of the parking lot.
Her manager then called her into his office later that same day, she said.
Cheney said that after the manager listened to her side of the story and asked if she would come to him with any problems in the future — she said she wouldn't because of his earlier inaction on the same issue — the manager told her she was fired.
When she asked once again to be told why she was fired, he said she was fired for being rude to a customer, Cheney said.
'My phone has not stopped ringing'
Since CBC broke the story, Cheney said she's been inundated with calls of support.
"My phone has not stopped ringing since the news yesterday," she said.
"I'm feeling overwhelmed by all the support of people, and I just think it's amazing that people have contacted me and shown their support, and I appreciate it very, very much."
She said she has retained an employment lawyer, Robert Monti.
Monti said he believes it's a clear case of wrongful dismissal.
"One of my colleagues was in a Shopper's Drug Mart recently where an animal was left in a car, and an announcement came over the PA system … saying that if you were the owner of such and such car with such and such license plate, get out to your car within the next minute or we're going to break the window," Monti said.
"So that was a completely different corporate response, and an appropriate one."
Wal-Mart says Cheney wasn't fired for trying to help dog
After issuing a statement Tuesday that didn't go into detail about Cheney's case, Wal-Mart issued another statement Wednesday.
"The associate in question was absolutely not let go for trying to help a dog in a locked car," the statement reads. "The decision to dismiss an associate is one that we take extremely seriously and must follow a comprehensive process. However, out of respect for the associate and for privacy reasons we cannot provide specifics about why this associate was let go."
The statement also said Wal-Mart donates to SPCAs, humane societies and animal shelters, and that signs will be put up at Wal-Mart stores across Canada warning customers about the dangers of leaving kids and pets in hot vehicles.
Cheney, meanwhile, said Thursday that she hadn't yet been contacted by Wal-Mart since she was fired.
"I knew something would happen when I contacted CBC, I didn't expect it to go this far or reach so many people," she said about the public's reaction to her story.
"It's great that the story's out there," she said.
Cheney said she plans to start looking for a new job next week.