The Association of Garda Sergeants and Inspectors says it will consider taking industrial action over the Government's refusal to grant it the right to strike.
The AGSI has told Minister for Justice Charlie Flanagan that the failure to grant it trade union status was discriminatory and contrary to an EU social rights committee decision, which was later recognised by the Council of Europe.
Middle-ranking gardaí also say there is a "chronic shortage" of supervisors to monitor the increased number of gardaí being recruited.
The AGSI said more than 160 more sergeants are needed immediately and have warned that unless the Government allowed for more promotions then the malpractice exposed by the O'Higgins Commission will re-emerge.
It pointed out that even in Bailieboro Garda Station, the focus of the commission's work, there are still not enough sergeants to supervise the gardaí there.
It said that despite the recruitment of additional gardaí by the Government, there are not enough sergeants and inspectors to supervise the additional intake.
The association says the Government imposed employment control framework limits on the number of sergeants to 2,000 - a figure it said is insufficient to supervise rank and file gardaí.
It also pointed out that at present the number of sergeants is more than 160 short of that figure with another 365 eligible to retire.
The AGSI says there are shortages of sergeants in almost every garda division in the country and a current dispute between the Government and senior officers is delaying further the promotion process.
We need your consent to load this rte-player contentWe use rte-player to manage extra content that can set cookies on your device and collect data about your activity. Please review their details and accept them to load the content.Manage Preferences
AGSI President Antoinette Cunningham said the last time accelerated recruitment was not matched by an increase in supervisors, garda malpractice and serious errors in criminal investigations were exposed, which led to the O’Higgins Commission of Inquiry.
Speaking on RTÉ's Morning Ireland, Ms Cunningham said that recent recruitment means sergeants are supervising up to 12 probationary gardaí, in addition to doing their own job.
She said that the AGSI will be asking Minister for Justice Charlie Flanagan to increase the numbers in the sergeant and inspector rank.
Over the next three days, the association's conference is due to discuss a number of motions, including issues of wellness and welfare at work.
There will also be calls to fully resource the public order unit, to properly equip all members to deal with serious weather events, such as Storm Ophelia, as well as a call to fill the vacancies for 24 forensic collision investigators nationwide.