Some in the travel industry are fearing a 'Trump Slump' — a drop in tourism following President Trump's executive order banning citizens from seven predominantly Muslim countries from entering the U.S.

Industry experts say it's too early to tell if such a slump will materialize. But the Pennsylvania Convention and Visitors Bureau in Philadelphia believes it has already lost one convention because of perceptions that potential participants may not be able to get into the country in the future.

Alethia Calbeck, director of communications at the Philadelphia Convention & Visitors Bureau, said one organization took a pass on Philadelphia in favor of holding their annual event in either Canada or Mexico.

"We were up for a piece of business and the organization decided to not have its meeting in the United States," Calbeck said. "They have a largely international audience and wanted to be sure everyone would be able to attend their meeting."

Calbeck declined to identify the group, which officials described as fairly large, with about 3,000 members. The financial impact would have been about $7 million for Philadelphia, officials said.

Since the ban was first announced, searches for incoming flights to the U.S. from international locations has declined as much as 17%,  the travel guide Frommers reported. 

"A drop of that magnitude, if continued, would reduce the value of foreign travel within the U.S. by billions of dollars," the website reported. Jobs dependent on tourism dollars — such as hotels, restaurants, transportation, stores, tour operations, and travel agencies — would be hit hardest.

Perry Flint, head of corporate communications for the International Air Transport Association, said it is too early to see if the travel ban has directly affected airline reservations.

"We don't have any data to show that," said Flint.

In a Q&A with Travel Weekly on Wednesday, David Scowsill ,the CEO of World Travel & Tourism Council, said the president's approach to security could bring about a long-term slump in tourism.

Scowsill said, "there is a trend of people from around the world not coming to the U.S. at this period in time. It is not dramatic at the moment. It is somewhere around the 4% to 5% range."

International travel generated an $88 billion trade surplus in 2016, according to the U.S. Travel Association.  International travel spending directly supported more than 1.1 million American jobs in 2015, with each traveler spending an average of $4,300 per trip.