Sumburgh Airport on Shetland and Kirkwall Airport on Orkney are shut today on day two of air traffic controller strikes get in a dispute over pay.
Tomorrow there will be walkouts at Stornoway, Benbecula and Dundee airports.
Prospect union members resumed industrial action after rejecting a revised pay deal from Highlands and Islands Airports Limited (Hial).
Inverness Airport was shut on Sunday, the first day of the latest 24-hour strikes.
Air traffic controllers previously went on strike on May 23, when the six airports were shut for 24 hours.
Hial said the offer rejected by air traffic controllers comprised a retention allowance which would have seen them benefit from an additional £10,000 over a five-year period.
Managing director Inglis Lyon said previously he "deeply regrets the inconvenience and upset to hundreds of passengers affected by the strike action".
He called on Prospect to resume talks to find a resolution to the dispute as soon as possible and claimed the union is asking for a pay increase "far in excess of what we are able to afford".
Prospect national secretary Richard Hardy said the strikes are a "last resort".
"Hial and Scottish ministers have left our members with no option but to strike," he said previously.
"Strike action is by its nature disruptive but if we are to safeguard the long-term future of air services in the Highlands and islands we have to start paying air traffic controllers a fair wage."
Hial is a public corporation wholly owned by the Scottish ministers.
A Scottish Government spokesman has said the Government encourages both parties to resolve the dispute as it is "clearly not in the interest of passengers or the communities served by Hial airports".
