The National Distribution Union says it is appalled that public money has been used to spy on unions.
Christchurch man Rob Gilchrist, who is said to have been passing on information about people involved in activist organisations such as Greenpeace, may also have been spying on unions.
The National Distribution Union has filed an official information request with police for its file.
Secretary Laila Harre says it looks as if police are using public money to indulge in a bit of old-fashioned, right-wing paranoia.
Ms Harre says she supports calls by other unions for a public inquiry into the actions of the police Special Investigation Group.
Among the unions upset at the police action is the Maritime Union, which says it is considering strike action unless it gets an apology from police.
Seven other unions were also targeted, according to one media report.
Maritime Union general secretary Trevor Hanson says workers will not permit it to be treated as a criminal organisation by the state.
Mr Hanson said he had received calls from members throughout the country on Friday morning because the union was publicly named as being on a police spy list.
Mr Hanson said he is taking legal advice, and added that the union supports calls for a commission of inquiry into the Special Investigation Group.
The Unite Union has called for a full public inquiry into the Special Investigation Group.
Police Commissioner Howard Broad has given assurances that Mr Gilchrist was reporting only on individuals, not groups.
But Unite Union general secretary Matt McCarten says he has emails showing that unions were also being watched.
Mr McCarten says the actions of the police spy unit have clearly gone well beyond any legal mandate, making an inquiry neccessary.
