Flights in and out of Shannon airport were delayed or diverted last night as air traffic controllers refused to fill in for a sick colleague as part of an ongoing unofficial dispute over staffing levels.
The Irish Aviation Authority expressed anger over the "wildcat" industrial action and urged controllers to desist.
Eleven flights were affected from 7pm onwards, said the Irish Aviation Authority (IAA), with departing flights delayed until after 9pm and arrivals - mostly Ryanair flights - diverted to Cork.
An Air France flight to Paris due to depart at 7pm, left eight minutes early last night and avoided a two hour delay.
The problems arose when one of the two controllers rostered to work in Shannon's tower called in sick.The tower is expected to operate as normal today.
The IAA said the action was at odds with commitments made by controllers after discussions with the Impact trade union.
"This is the third time in little over two weeks that Impact has given an assurance that their members would return to normal working and it is also the third time that air traffic controllers have reneged on this commitment," the authority said last night.
The two sides are due back in the Labour Relations Commission today. The controllers say they are being asked to perform too much overtime due to a shortage of qualified staff. The IAA argues that there are sufficient staff to meet workloads, and more employees are coming into the workforce all the time.