The Road Safety Authority has urged anyone with a driving test booked for next Wednesday afternoon to rebook it, due to strike action.
Driving testers are to strike from 2pm next Wednesday in a row over the hiring of new contractors by the RSA.
Trade union IMPACT said the move is in direct contravention of a Labour Court ruling which recommended the recruitment of a reserve body of testers to avoid a backlog in test applications.
IMPACT confirmed all driving testers would down tools from 2pm on April 2.
The RSA said it was extremely disappointed with the stance taken by IMPACT, and insisted it was acting in accordance with the Labour Court.
IMPACT assistant General Secretary Denis Rohan said the workers had no choice but to strike.
"We felt we had no option other than to take this action to emphasise …that we're opposed to the out-sourcing of this work," he said.
"What we have attempted to do is to limit the inconvenience to a half a day initially, and we hopefully the employer will see sense and engage with us in discussions to try and resolve it, even between now and then."