The new American Airlines just hit a speed bump called the Justice Dept.

The U.S. Justice Department is taking depositions as part of a probe into a planned merger of American Airlines Inc and US Airways Group Inc that would create the world’s largest airline, three sources close to the discussions told Reuters.

The sticking point in talks between the Justice Department and the companies is whether the airlines will agree to sell slots, take off and landing rights, to reduce their dominance at Reagan National Airport outside Washington, D.C., according to one source.

The three sources spoke privately to protect business relationships.

US Airways announced on February 14 that it planned to merge with American, which is emerging from bankruptcy, to create an $11 billion airline. The deal requires the approval of the U.S. Justice Department and the Department of Transportation. The companies hope to wrap up the merger by the end of September.

American Airlines and US Airways declined comment.

The fact that the Justice Department is taking sworn testimony in the form of depositions indicates it has concerns that the proposed merger creates antitrust problems. Depositions will be needed if the agency approves the deal with conditions or, in rare cases, if it decides to try to stop it. The department could also decide to approve the merger without requiring asset sales.

Depositions preserve testimony if the department decides to challenge the merger, said Robert Doyle, an antitrust expert with Doyle, Barlow and Mazard PLLC.

If the deal is approved, the new airline would have 68 percent of the slots at Reagan National, far more than Delta Air Lines Inc with 12 percent, United Airlines with 9 percent and the 11 percent held by other airlines, according to a report by the U.S. Government Accountability Office.

The companies have pushed back hard against any suggestion that takeoff and landing slots at Reagan National be sold.

US Airways CEO Doug Parker told lawmakers in congressional testimony last week that requiring the combined company to surrender slots could mean fewer flights to small and medium-sized cities.

Justice Department spokeswoman Gina Talamona said only that the agency’s investigation was ongoing.

Antitrust experts have said the Justice Department could request divestitures of some slots at Reagan National and a small number of other airports. Outside these hubs, the carriers fly different routes for the most part.

In late May, more than 100 members of Congress asked U.S. regulators to allow the new American to keep all the slots at Reagan National. The airport is used by many members of Congress to travel to and from their home districts.

The U.S. airline industry has undergone five years of rapid consolidation. Delta acquired Northwest Airlines in 2008, United merged with Continental in 2010 and Southwest Airlines Co  bought discount rival AirTran in 2011.

With fewer carriers competing, ticket prices have risen. The average fare rose about 8 percent to $375 in the third quarter of 2012, compared with $346 in 2008, according to the U.S. Bureau of Transportation Statistics.

Editing by Andre Grenon. Copyright (2013) Thomson Reuters. Click for restrictions.