Last week, Iberia petitioned a court to ban strikes by pilots and cabin crew planned over the next few months and to seek compensation for 12 days of strikes held between December and March.

The strikes were briefly called off in March and pilots went into talks with the company. But negotiations broke down.

Pilots union SEPLA says Iberia Express is a threat to jobs and conditions, but the company says it is vital to increasing profitability.

Iberia estimates the strikes will cause damages of 3 million euros ($3.92 million) per day.

Iberia's Web page showed more than 150 flights were cancelled on Monday, including destinations within Spain, around Europe, and to Latin America.

Pilots, who plan to strike every Monday and Friday until July, say Iberia's new low-cost service contravenes deals struck when Iberia and British Airways merged to form International Consolidated Airlines Group.

They say 8,000 jobs will be lost as Iberia moves a few dozen airplanes to the low-cost subsidiary from its full-service airline.

IAG and Iberia say starting the new airline is the only way to make the loss-making Spanish unit profitable.

European airlines are battling soaring fuel prices, weak demand from cash-strapped passengers and the burden of new taxes on air travel as well as fierce competition from low-cost carriers such as Ryanair (RYA.I) and EasyJet (EZJ.L).

Iberia Express is designed to complement Iberia's more profitable long-haul flights, flying to 17 national and European destinations including Dublin, Naples and Amsterdam. ($1 = 0.7655 euros)

(Reporting By Fiona Ortiz; Editing by Jacqueline Wong)

• A Permanent Economic Emergency