The association says its members have not received training in using the new drug testing devices
Garda sergeants and inspectors say it may be some time before roadside drug testing is actually carried out by the force - despite the announcement that it can commence from tomorrow.
The new legislation comes into effect from midnight, but the AGSI - whose annual conference has been taking place this week - says its members have not received training in using the drug testing devices.
Senior Gardaí say the traffic corps have been fully trained in the use of the machines - and that will be rolled out to all officers in the coming weeks.
General Secretary of the AGSI John Jacob says the public may have been given the wrong impression.
He argued: "They should have cautioned people that the Gardaí at this point of time - from what I can understand from my colleagues at the conference - that we don't have the capacity at this point in time to deliver that service."
The new roles allow Gardaí to carry out Mandatory Intoxicant Checkpoints (MITs), where officers will be able to test a sample of a driver's saliva for the presence of drugs such as cocaine, heroin, Valium and cannabis.
Anyone found to be over the legal threshold for cocaine, cannabis or heroin faces a minimum one-year disqualification from driving.
Road Safety Authority Chief Executive Moyagh Murdock said she has 'no doubt' that the new tests will have a 'profound and positive impact' on road safety.