ASTI members have voted to reject the public service pay agreement.
It's comes amid concerns over its failure to address the issue of lower pay for staff recruited since 2010.
51.5 percent of those who voted rejected the deal, while 48.5 percent were in favour.
The turnout was 64 percent.
The ASTI President, Celbridge resident Ger Curtin, said that by rejecting the agreement, members continue to stand up for their most vulnerable colleagues.