Staff strike grounds planes at six Scottish airports
Air traffic controllers employed by Highlands and Islands Airport Limited want a 10% raise.
Six airports have been closed due to a strike by air traffic controllers involved in a pay dispute.
Airports in Inverness, Dundee, Benbecula and Stornoway in the Outer Hebrides, Sumburgh in Shetland and Kirkwall in Orkney will be shut throughout Thursday.
Staff at Highlands and Islands Airport Limited (Hial) rejected a 2% pay rise offered last year - calling for at least a 10% hike.
Union Prospect claimed its members did not want to take industrial action, but have been left with no choice after running "out of patience" with Hial.
However, Hial believes its air traffic controllers are well paid and claimed it has been fully committed to resolving the dispute.
'Unless Prospect temper its claim and Hial is afforded flexibility around the implementation of the Scottish Government's public pay policy, I do not see a quick resolution to this dispute.'Inglis Lyon, Hial managing director
In a statement issued on Monday, Hial managing director Inglis Lyon said: "We sincerely regret this escalation of the pay dispute by Prospect members and apologise for the inconvenience that this has caused our customers.
"We continue to work closely with our airlines to mitigate the effects of strike action and I wish to thank them and all our staff who have worked extremely hard to implement contingency measures.
"Throughout this process, Hial has been fully committed to resolving this dispute.
"We are disappointed that our efforts to provide possible solutions have been rejected by Prospect and its claim has not altered and remains a wage increase of at least 10%."
Mr Lyon said the airport operator - a public corporation wholly owned by Scottish ministers - is bound by Scottish Government pay policy and cannot negotiate a separate settlement.
He added: "We believe Hial air traffic controllers are well remunerated and have already accepted a pay increase backdated to April 2018.
"I urge the union to consider the best interests of all their Hial members, our communities and those with a stake in the long-term future of air services in the Highlands and Islands and moderate its claim to help us jointly resolve matters.
"Unless Prospect temper its claim and Hial is afforded flexibility around the implementation of the Scottish Government's public pay policy, I do not see a quick resolution to this dispute."
The controllers have been working to rule since the beginning of April.
Amid the dispute, a plane was forced to depart from Orkney to Edinburgh without air traffic control clearance last month.
The union argued that start-up clearance was denied as it would have involved a controller having to work beyond their shift - contravening "very strict" rest periods.
Prospect initially agreed to suspend a strike planned for April 26 to allow for talks.
However the discussions, facilitated by the Advisory, Conciliation and Arbitration Service (Acas), broke down earlier this month and a strike date was set for Thursday.
Last week, Prospect accused Hial and Scottish ministers of being involved in an "unedifying blame game" which will do nothing to resolve the dispute.
David Avery, Prospect negotiations officer, said: "My message to those suffering disruption to their flights is clear - ministers and Hial have the power to end this strike today and to end this disruption but are choosing not to.
"Worse, they are choosing to pass the buck and blame each other for the failure of negotiations.
"With no-one stepping up to take responsibility there is no end in sight for this action.
"Ministers need to step in now and end this blatant dereliction of their duty."
The remaining airports operated by Hial - Wick John O'Groats, Barra, Campbeltown, Islay and Tiree - are expected to remain open.
A Scottish Government spokesman said: "It is disappointing the union is taking strike action, which will clearly impact passengers.
"We continue to encourage both Prospect and Hial to return to discussions around a retention allowance for air traffic controllers and to work towards a resolution to the pay dispute.
"In the face of the UK Government's continued budget cuts, the Scottish Government delivered a distinctive and progressive pay policy for 2018-19 - one which is fair, supports those on lower incomes and protects public sector jobs and services while delivering value for money for the people of Scotland."