Driving testers are going on strike this afternoon.
It means anyone who had a test booked after 2pm has had it rescheduled.
The IMPACT trade union is accusing management at the Road Safety Authority of planning to breach a Labour Court ruling, which set out a process for the recruitment of reserve testers.
The union's Assistant General Secretary Denis Rohan says there's likely to be more action after today.
"It's the first in a series of stoppages," Mr Rohan said.
"But I should say also that it's the first time in the 50 years of driving testing that we've had a dispute of this nature.
"That, in itself, shows you the lengths to which we had to be pushed prior to taking this action."