Dozens of flights to and from French airports, as well as those flying in French airspace, were cancelled on Thursday as the USAC-CGT union went on a one-day strike.
Ryanair has cancelled 56 flights for the day - the full list of which can be seen here, while EasyJet cancelled 24 flights in France, while Aer Lingus cancelled six.
France's Civil Aviation Authority, DGAC, did not actually recommend any airlines to cancel flights, but warned passengers to expect delays.
Ryainair wrote that further delays and cancellations "were likely", and urged its customers to sign a petition against what it said were "tiny groups of Air Traffic Control (ATC) unions going on strike and closing skies over Europe".
Passengers will be informed of any cancellations, but are advised to check online before heading to the airport in all cases.
The air traffic controllers called the strike in protest of the controversial labour reforms, that have seen demonstrations and strikes all over France in the past few months.
The airport workers are also unhappy over their salary levels.
The USAC-CGT union had threatened a three-day strike for earlier this month, but it was called off at the eleventh hour.
Also on Thursday, the head of the far-left CGT union will lead yet another demonstration in Paris against the labour reforms, after the protest was initially banned by police.
"After tough talks with the interior minister, the union and student organisations obtained the right to demonstrate on a route proposed by the interior ministry," CGT head Philippe Martinez said on Wednesday.