MADRID (AP) — The city of Madrid has asked Spain's anti-trust watchdog to investigate whether Uber's new airport transport service violates fair competition laws.

Uber, the San Francisco-headquartered mobile ride-hailing service, offers rides from 15-29 euros ($17-$34) from Madrid's airport to the city center. The fair for taxis is set at 30 euros ($35).

In a statement Saturday evening, Madrid's city hall says "(Uber's) tariffs may violate several articles of the Law of Unfair Competition and consumer rights if they are below the cost of providing the service."

Taxi drivers in Spain went on strike in March and in May to protest what they say is unfair competition from Uber and the similar Madrid-based car service Cabify.

Unions claim these companies flout a law stipulating that there should be one private company vehicle for every 30 taxis.