Flights have been cancelled and hundreds of passengers delayed at the start of three days of industrial action by French traffic control employees.
British Airways and easyJet flights from Gatwick, Heathrow and Luton airports are being affected.
At Gatwick, passengers have been experiencing delays averaging 50 minutes.
The airport has advised all passengers to ring their airlines for updates,
A spokesman for easyJet said 32 flights scheduled to take off or land at British airports today have been cancelled.
British Airways did not disclose how many flights would be affected by the strikes, but said it was doing "all we can to minimise disruption to customers affected".