The Association of Garda Sergeants and Inspectors has insisted its members cannot be tested for drugs without a reason.
The association was responding to the announcement that random drug testing of all garda personnel, including administrative staff, will begin in six months.
It said it had not been informed about the drug testing process and has not agreed to the garda policies on substance abuse.
Garda Headquarters said a procedure document will be issued in advance of drug testing and that compliance with the garda drugs policy is mandatory for all personnel.
The announcement by the Garda Anti-Corruption Unit that all gardaí, civilian staff, recruits and probationers would be subject to drug testing has been contested by the organisation representing middle-ranking gardaí.
The Garda's Substance Misuse controlled drugs policy has now been published and states not only that drug abuse is not tolerated, but also that "testing of garda personnel and all prospective employees for drugs within the workplace is to be introduced".
It says the policy has been legal and human rights screened in terms of the respective obligations placed on gardaí.
The assistant commissioner in charge of governance and the chief superintendent in charge of the anti-corruption unit have both said the policy and testing apply to all garda employees and prospective employees.
AGSI General Secretary Antoinette Cunningham has insisted that drug testing will only be "with cause" and that there must be a report, suspicion or reason before a test can be carried out on a sergeant or inspector.
Garda Headquarters has dismissed this claim.
In a statement, it said compliance with the Garda Substance Misuse Policy, which includes drugs testing, is mandatory and that when testing is introduced it will be "done on a random basis".
A garda spokesman also clarified that "random" testing is by definition without prior warning or cause.
Speaking on RTÉ's Morning Ireland, Ms Cunningham said the association is not opposed to random drug testing, but while tentative discussions have taken place with Garda management, more engagement is needed.
The Garda Representative Association has said it has not agreed any policy and was not consulted.
The association, which represents rank-and-file gardaí, also said it certainly had not signed off on anything.
GRA Vice President Brendan O'Connor said members would not have a problem with "proportionate random drug testing" but yesterday's announcement came as a shock.
He said that gardaí are on the frontline in the fight against drugs and have no time or regard for anyone involved in criminal activity or association with those who wreak havoc on communities.
Speaking on RTÉ's Today with Claire Byrne, he said management had indicated that they were going to test around 5% of the workforce, but media reports suggest that every guard would be subject to drug testing.
The AGSI says it has written to the Garda Commissioner seeking clarity on reports that all garda personnel are to be drug tested within the next six months.
Antoinette Cunningham said the association is seeking "urgent clarity" in relation to the announcement that random drug testing of all garda personnel, including administrative staff, will begin in six months.
Ms Cunningham also said AGSI supports any initiative that builds public trust and confidence in An Garda Síochána.
"We realise all that all the members of AGSI have to be beyond reproach when it comes to matters such as drug testing in An Garda Síochána.
"For that reason we have had some tentative discussions with Garda management around drug testing with cause and around random drug testing for around five per cent of the workforce."
She added this is something the AGSI would support.
An Garda Síochána said the drug testing will be done on a random basis and that "by definition, random means without cause".
It added that "the misuse of controlled drugs by Garda personnel will not be tolerated" and that compliance with the Garda Substance Misuse (Controlled Drugs) Policy is "mandatory for all Garda personnel".
The policy document also says that a procedure document will issue in advance of the commencement of drug testing.
Additional reporting Aengus Cox