Iberia said Monday it had rescheduled flights for most passengers affected by the strike.
Pilots union SEPLA says it will strike again Wednesday, forcing the cancellation of another 104 flights.
Iberia says the strikes will affect 23,000 passengers on long-haul, medium-haul and domestic flights.
SEPLA says the creation of Iberia Express will lead to job losses.
But Iberia, Lineas Aereas de Espana S.A., denies there will be job cuts among its 1,600 pilots.
Iberia Express is to take over loss-making domestic and medium-haul routes and will employ lower-earning, newly-hired pilots and attendants.