The Garda Representative Association has rejected the terms of the Lansdowne Road Agreement.
It was recommended by the GRA leadership to accept the terms.
60% of the members of the rank-and-file officers' union took part in the ballot - with 87% voting 'No' and 11% voting 'Yes'.
The GRA represents 2,000 mid-ranking gardaí around the country.
The GRA's central executive committee will meet next week to discuss the outcome of the vote.
It follows the Association of Garda Sergeants and Inspector's rejection of the same pay deal earlier this month.