Passengers travelling through Dublin airport could face disruption for an indefinite period due to a lack of air traffic controllers.
As of 4.20pm, there had been no delays and the Irish Aviation Authority (IAA) said it was optimistic there would not be any today.
IAA spokeswoman Lilian Cassin said the situation would be monitored hourly and warned: "If we find ourselves understaffed, in the interest of safety we will have to impose restrictions, and that may result in delays to aircraft.
Around 100 controllers working at the State's busiest airport yesterday withdrew from voluntary overtime arrangements due to what they say is chronic under-staffing.
The IAA issued a statement this morning accusing the controllers of taking unofficial action in breach of social partnership and their local agreement. The Impact trade union said the controllers are not engaging in industrial action, however, and are entitled to refuse overtime.
Ms Cassin said arrangements had been in place with controllers to work overtime when cover for staff off due to sickness or other reasons was needed.
"On an individual basis, those staff members have withdrawn their co-operation and flexibility," she said.
Impact and IAA management are due to meet today to discuss the matter.
Some new trainee controllers were recently recruited but will not be available until late next year due to the training needed.
The controllers have asked management to recruit qualified people from abroad or those who have retired or were laid off after the anticipated fall-off in travel following 9/11.
Ms Cassin insisted there was no staff shortage at the airport but said efforts to recruit qualified controllers on a contract basis had begun. It would take some months before successful applicants were trained, she added
An Impact spokesman said the controllers had no plans to escalate their action at this time.