The group representing Garda sergeants and inspectors says officers can’t be drug tested without a reason.
It comes after it was announced that all Gardaí would be subject to random drug testing.
Under new proposals, drug testing will start for all Garda personnel in approximately six months.
Those who test positive for a controlled substance will face dismissal and possible prosecution.
The Association of Garda Sergeants and Inspectors (AGSI) says it wasn't informed of the new system.
AGSI General-Secretary Antoinette Cunningham said: "AGSI supports any initiative that builds public trust and confidence. We recognise that members of An Garda Síochána should be above reproach in the exercise of their duties.
"For that reason we broadly support the introduction of polices which can enhance these matters."
However, she said: "The AGSI are unaware of plans to drug-test all Garda personnel within six months and from early discussions on these issues, understood that it would be random drug testing for approximately 5% of the workforce and 'with cause' testing.
"We call on Garda management to urgently re-engage staff associations in a consultation process on these very important issues."
Deputy Garda Garda Commissioner, Paula Hilman, has said staff members will receive further details on the plan soon.
"The finer detail of that will be published and will be communicated by the Anti-Corruption Unit.
"But I know, and I'm sure, that they will continue to engage with our staff associations as they work out the finer details".