Flights between Ireland and Scotland were cancelled today as the return of the Icelandic ash cloud threatened travel chaos.
Both Ryanair and Aer Lingus halted services to Glasgow, Edinburgh and Aberdeen until at least 1pm.
Ryanair said it strongly objected to the disruption under orders from the Irish Aviation Authority (IAA).
The IAA said last night that it did not expect any disruption at Irish airports during most of today.
But it later ordered flights to Scotland to be pulled as forecasters predicted that the volcanic plume, billowing from Iceland's Grimsvotn volcano, would hit Scotland and Northern Ireland during the morning, with much of the UK being covered by midday.
Ryanair insisted there was no basis for the flight cancellations.
It will meet the IAA this morning to have the restrictions removed as a matter of urgency, according to its website.
"Ryanair believe that there is no safety risk to aircraft on fights operating to and from Scotland and, together with other airlines, will be complaining to the Transport Minister and regulatory authorities about these latest and unnecessary cancellations," a company spokesman said.
Both Ryanair and Aer Lingus have advised intending passengers to contact their airline or check the company websites ahead of travelling to airports.