In a challenge to boycotts of Israel, the U.S. government has found that Kuwait Airways unlawfully discriminated against a passenger traveling on an Israeli passport by refusing to sell him a ticket for a New York to London flight.

Eldad Gatt, an Israeli citizen, complained to the Department of Transportation that in 2013 he was unable to buy a ticket from John F. Kennedy Airport to London Heathrow Airport through Kuwait Airways because the airline's online booking system prevented him from selecting Israel as his passport-issuing country.

The department investigated and initially rejected Gatt's discrimination complaint, according to a statement and letter provided by transportation officials. But when Gatt appealed the department's decision, the case was reopened and the department ultimately concluded that the airline had violated a different federal law than the one initially cited by Gatt.

"We considered Mr. Gatt's claim upon an alternative ground ... which holds that an 'air carrier or foreign air carrier may not subject a person, place, port, or type of traffic in foreign air transportation to unreasonable discrimination,'" Blane Workie, DOT's assistant general counsel for enforcement said in a letter to the airline.

By refusing to transport Israeli citizens to and from the U.S. and a third country that accepts Israeli citizens, in this case the United Kingdom, the airline is in violation of the law, the letter said. "We expect (Kuwait Airways) to sell tickets to and transport Israeli citizens between the U.S. and any third country where they are allowed to disembark based on the laws of that country," Workie said.

Transportation Secretary Anthony Foxx said the case is a warning that "any airline that wishes to operate in the U.S. should know that we will not tolerate discrimination of any kind in our skies."

The airline explained that it's against the law in Kuwait to do business with any Israeli citizen or company, and that punishment for a violation could result in imprisonment and hard labor, according to the department.

"We do not find the interest of Kuwait in the enforcement of its laws in this case to be greater than the interest of the United States in the enforcement of its laws," the letter said. "It is our view that the U.S. interest in providing nondiscriminatory access to air transportation to an individual traveling from the U.S. to a third country that allows that individual's entry is greater than Kuwait's interest in applying its economic boycott of Israel."

The department said it is aware of another, similar complaint.

The department has given the airline 15 days to respond. A range of enforcement actions are possible, beginning with civil penalties. Kuwait Airways officials didn't immediately respond to a request for comment from The Associated Press.