The union blasted an incident in which an officer in riot gear pushed and verbally abused a cameraman on Sunday night when police were clearing protesters from Mong Kok.
An officer also hit the TV camera.
The union said on Tuesday that the actions of the police are seriously threatening the safety of media workers.
It added that by pushing journalists and using batons to block cameras, officers may be violating Police General Orders that prohibit them from obstructing the work of the media.
The union accused the force of being unprofessional and displaying animosity towards journalists.
It urged Police Commissioner Stephen Lo to order officers to stop hindering the work of the press.