The Spanish airline Iberia grounded 150 flights Monday as pilots struck to protest the start-up of the low-cost carrier Iberia Express.

The Iberia pilots say they plan to strike 30 times — every Monday and Friday between now and July 20. The pilots said the start of the new airline is a threat to their jobs and working conditions, and violates labor agreements forged when Iberia merged with British Airways.

Low-cost Iberia Express started operations late last month. Its shorter routes to Spanish cities and some European destinations are designed to supplement Iberia's longer flights to other locations.

The owner of the airlines said it had to create the low-cost carrier to increase its profitability.