NEW DELHI, April 10 (Reuters) - Two letters showed that Dubai has imposed restrictions on foreign airlines, allowing them only one daily flight to its airports until May 31 because of the Iranian crisis, raising concerns about revenues for Indian carriers that had planned more flights than airlines in other countries.

In a letter to the Indian government on March 31, the Association of Indian Airlines, which represents major airlines IndiGo, Air India and SpiceJet, asked New Delhi to pressure Dubai authorities to lift the restrictions and, if unable to do so, to consider taking similar measures against Dubai airlines, such as Emirates and Flydubai.

Indian airlines are already under financial pressure due to high fuel prices and longer flight routes to Western destinations after being barred from using Pakistani airspace since last year following military tensions between the two neighboring countries.

In a private email to airlines dated March 27, seen by Reuters, Dubai Airports said airlines would be allowed one round-trip flight per day to Dubai International Airport, usually the world's busiest international travel hub, and the smaller Al Maktoum International Airport during the summer season between April 20 and May 31, extending restrictions imposed after the start of the war.

"Airlines will remain restricted to one round-trip flight per day, until capacity allows for more... Additional take-off and landing slots will be allocated if capacity becomes available," she said.

The Association of Indian Airlines told the New Delhi government that the restrictions do not apply to Dubai-based airlines such as Emirates and Flydubai, creating an uneven competitive environment that could lead to "significant" revenue losses.

Dubai Airports and the Dubai government media office did not respond to repeated requests for comment. Flydubai said its flight schedules had been approved by the relevant authorities. Emirates did not respond to a request for comment.

These measures come after Emirates and other Gulf airlines have long complained about India's bilateral air services agreements, which limit the number of seats that can be made available between the two countries. Indian authorities have said these agreements protect Indian airlines in a highly competitive market.