"We're boxing animals. Where's Sarah McLachlan?" the man can be heard saying, apparently mocking the singer's association with cruelty prevention advertisements.
The dog's head is snapped to the right and left as she lands almost a dozen blows in the 13-second clip; he lets out a yelp as she lands a final particularly hard left hook.
"I hit him so hard I felt that through..." she says as the video suddenly cuts off and the man chuckles.
After receiving an "overwhelming" number of phone calls and emails about the clip, Idaho Humane Society said it had opened an investigation and sent it to the prosecutors office.
It said the woman may now be charged with beating and harassing animals.
"The Idaho Humane Society works to protect all animals from abuse," it said on Facebook. "We also believe that because domestic animals are a product of human intervention, we have a very special obligation to them in regard to humane treatment and responsible stewardship."