The strike, which is expected to affect 1,220 flights and cost the airline $13.3 million per day, is the longest ever staged by the airline's workers, who are battling a plan to cut over 3,800 jobs.
The airline has rejected a proposal put forth by pilots to save jobs that included a 26 percent cut in pay, ThinkSpain reported.
Iberia has found alternative flights for 85 percent of the passengers who would have been stranded by the strike. That meant 60,000 travelers so far have solutions, while 10,000 others had to be given refunds, ThinkSpain said.
The strike is the first of several five-day work actions planned. It will affect flights scheduled by Iberia Express, Air Nostrum and Vueling, as well as Iberia flights. Two more are expected before the end of March.