Staffordshire Police is hoping to save 5,500 police hours a year by getting volunteers from the community to regularly clean its fleet of vehicles.
The idea is the latest cost-cutting idea from cash-strapped forces, which are also seeking people to work for free completing tasks such as gardening and translating.
However, it has raised concern among police officers and staff, who fear volunteers could pose a security risk.
Staffordshire Police launched its appeal for volunteers to clean cars, act as interpreters and hand out crime-fighting leaflets two weeks ago.
A spokesman said it had received a "number" of applications but could not say if any of the jobs had been filled.
The job advert posted by the force seeks car washing volunteers who would also be required to check equipment in cars and replace faulty items such as traffic cones and flashing lights.
The force also wants unpaid interpreters to work alongside officers on patrol and helpers for crime prevention campaigns.
Ben Priestley, of Unison, which represents police staff, told the Daily Mail: "The public will be very concerned that this vital work is being done by untrained volunteers who will not be subject to the same high standards of professionally employed police staff."
PC Andy Adams, of Staffordshire Police Federation, said: "With this sort of thing they may look at other roles in the organisation where they can push it a little bit further.
"I would like to think that all these people are properly vetted and accredited but that will of course cost money."
All volunteers must be at least 16 and are to be vetted and given an induction course before they can start work, the force said.
Assistant Chief Constable Julian Blazeby said he thought local people would be "keen to get involved" in helping their local force.