The first of a series of strikes affecting six Scottish airports has begun.
Air traffic controllers employed by Highlands and Islands Airports Limited (Hial) have taken the action in a dispute about their pay.
Sunday’s strike involves Inverness Airport.
Further 24-hour strikes will take place on Monday at Sumburgh and Kirkwall and on Tuesday at Dundee, Stornoway and Benbecula.
The controllers’ union Prospect said the strikes were “a last resort”.
Hial’s managing director Inglis Lyon has apologised for the disruption the strikes will cause passengers.
The Scottish government, which owns Hial, has urged the company and Prospect to hold fresh talks to resolve the dispute.
A row about the air traffic controllers’ pay has been running for months.
Prospect has called for a staff pay rise of at least 10%, arguing that air traffic controllers in the private sector earn much more.
A work-to-rule has been in place since April and a 24-hour strike shut the six airports in May.
Hial’s latest offer earlier this month included an additional £10,000 over a five-year period. It was rejected in a ballot of the Prospect members.
David Avery, Prospect negotiations officer, said the union had sought to avoid taking strike action on dates that would disrupt major events.
Mr Lyon said Hial “deeply regretted the inconvenience and upset” to hundreds of passengers affected by the strikes.
He added: “We wish to find a resolution to this dispute as soon as possible and would urge Prospect to sit down with us once again to find some common ground on which we can arrive at a negotiated settlement.”
A Scottish government spokesman said: “Hial has been authorised to develop a retention allowance as part of the Air Traffic Management 2030 Strategy programme.
“We have been clear with both Hial and Prospect that any settlement must be in line with Scottish Public Sector Pay Policy.”