The national secretary of the National Distribution Union says police are wasting taxpayers' money by spying on legitimate union activities.
Laila Harre says an Official Information Act request to police about information held on the union has returned about 20 pages of material.
Ms Harre says the information, which includes excerpts of documents, is of no legitimate interest to police and could have easily been gathered by a member of the public.
She says the union is concerned police resources are being wasted on the surveillance of normal, legal activities.
Ms Harre says an inquiry is needed to address the amount of public funding being spent on surveillance activities.