The Biden administration said Thursday it is launching a broad investigation into the state of competition in air travel, including the effect of mergers and joint ventures between airlines.

The investigation is being handled by the Justice Department’s antitrust division and the Transportation Department.

The administration has successfully blocked three airline deals in the past four years, and President Joe Biden has criticized airlines for charging “junk fees.”

However, the timing of the Thursday's announcement — less than three months before Biden leaves office, and with the race to succeed considered a toss-up — casts uncertainty over the fate of the investigation.

Four airlines dominate the U.S. airline industry — United, Delta, American and Southwest. They are the product of mergers that eliminated several major airlines.

The airline industry says that there is plenty of competition, however. The industry points to Transportation Department data that shows average U.S. airfares have generally declined for many years, although that has been partly offset by higher fees for baggage, premium seats and other items.

In the second quarter of this year, the average ticket was $382, according to the government figures. That is down from $404 in the same quarter of last year and $438 in the same period of 2019, before the coronavirus pandemic.

The departments said they will also look into the way air travel is priced and sold, and airline frequent-flyer programs.

The agencies said they will take public comments until Dec. 23.