United Airlines is reportedly interested in a merger with American Airlines

United Airlines has reportedly floated a merger with American Airlines. United CEO Scott Kirby discussed the idea with President Donald Trump earlier this year, according to Reuters.

A potential tie-up would create the world's largest airline.

For years, domestic airlines have complained of unfair competition from foreign ones. “A lot of these international carriers coming in, they’re still subsidized to an extent by their government,” said Dan Bubb, a professor at the University of Nevada, Las Vegas.

Qatar Airways and Etihad, from the United Arab Emirates, have both been expanding their offerings to the U.S. Bubb said the influx may have contributed to this proposed merger between United and American.

“They're seeing these other airlines and saying, ‘Wait a second, they're gonna control our market. They're gonna price us out,’” he said.

A merger this big is sure to face antitrust scrutiny. American Airlines is the largest U.S. carrier by passenger volume. And United is near the top also, said Richard Aboulafia at AeroDynamic Advisory.

“The idea of them combining would be, well, tectonic,” he said.

Aboulafia said smaller mergers in the past haven’t caused major fare hikes. To avoid that here, regulators could determine which routes would become near-monopolies and require divestitures.

“Oh my God, such control over Chicago, LA. You've gotta give up half of those,” he said.

Some of those routes could end up in the hands of competitors like Delta, Aboulafia said.