Ground staff and cabin crew at Spanish flag-carrier Iberia have begun 15 days of strikes.
Workers are reacting to plans to lay off 3,800 workers as managers seek to return the airline to profitability.
The airline says the stoppages, to be staged over three weeks, will lead to more than 1,200 flight cancellations, including 236 on Monday.
Some 70,000 passengers are likely to be expected today.
However, a government decree on minimum services guarantees 90 per cent of long-haul flights, 61 per cent of medium-haul and 46 per cent of domestic flights will all operate.
Unions representing most Iberia workers, but not pilots, called the strikes between February 18th-22nd, March 4th-8th and March 18th-22nd.