The Association of Garda Sergeants and Inspectors (AGSI) is being urged by Minister for Justice Michael McDowell to participate in discussions on the creation of a Garda reserve.
AGSI president Joe Dirwan described the plans to create a 900-strong reserve by next September as a "mad hatter" scheme.
Mr Dirwan said the plan would lead to a voluntary corps with 24 hours training obtaining full garda powers.
Speaking after an AGSI national executive meeting, Mr Dirwan said reservists would have access to confidential information on the Garda's Pulse database.
Members were concerned that they could become "nursemaids" for the reservists, cleaning botched arrests and other incidents, Mr Dirwan said.
He also expressed concern for safety and discipline: "What will the Minister say to the members of the reserve and their families when they come under attack - as they inevitably will - and there is serious injury or even death?"
"We fear that the reserve will become a haven for people who are attracted by the idea of having police powers over their neighbours and of settling old scores under the pretence of police action."
Mr McDowell today denied the AGSI claim that the reserve was an attempt to get "policing on the cheap".
"It is in no way intended as a substitute for increased Garda recruitment, as the current recruitment of 2,000 extra gardaí clearly demonstrates," Mr McDowell said.
Garda Commissioner Noel Conroy is drawing up proposals for the duties and training and that all Garda associations would be consulted.
"The Garda reserve will be a source of local strength and knowledge. Reserve members will be given very carefully selected powers and duties, they will be properly trained for whatever they are asked to do, and they will always work under the supervision of regular members of the force," Mr McDowell said.
Provision for up to 4,000 reservists is contained in the Garda Síochána Act passed earlier this year. Mr McDowell said Oireachtas Justice Committee had visited the UK and the proposed force had cross-party support.