PETA was out in force, protesting the opening of "A Dog's Purpose," chanting "Dogs aren't props!"
Several dozen people planted themselves in front of the ArcLight in Hollywood ... some wearing dog costumes.
The protest was triggered by a TMZ video showing a trainer trying to pull the dog star -- who was clearly unwilling and upset -- into the water. Producers say it was a one off, where the dog actually liked jumping in but they changed the angle and that's why the dog freaked out.
It's unclear so far how the movie is doing ... and whether the protests had an impact on attendance.