A new ban on U.S. travel for nationals of seven Middle Eastern countries caught the airline industry unprepared, with flight crew from those states also barred from entering, the International Air Transport Association said on Saturday.

U.S. Customs and Border Protection (CBP) has briefed the global trade group that passport-holders from states such as Iran and Iraq, including cabin crew, will be barred entry to the United States, IATA said in an email to its member airlines, seen by Reuters. The email underscores airlines' confusion about the situation as well as the challenge some may face from crew scheduling.

Airlines also stand to lose business: for instance, around 35,000 travelers from Iran visited the United States in 2015, according to the U.S. Department of Homeland Security.

"Much of this development has come over the weekend and at a time when IATA's Facilitation team has been on duty travel. Unfortunately, our response has been slower than we would have preferred," the email said. "A number (of questions) have yet to be resolved."

The executive order by President Donald Trump bans travelers with passports from Iran, Iraq, Libya, Somalia, Sudan, Syria and Yemen for 90 days.

IATA was informed that lawful permanent residents of the United States - or green-card holders - from those countries are not included in the ban. However, a Trump administration official told reporters that green-card holders from the countries need to check with a U.S. consulate to see whether they can return, causing some confusion for airlines, which still plan to follow CBP guidance. Qatar Airways said earlier on its website Saturday that passengers would need a green card or diplomatic visa to enter the United States.