A new rule regarding air travel fee transparency enacted by the U.S. Transportation Department earlier this month has sparked outrage among major U.S. airlines — and now the companies are suing the government to block the new order.

The lawsuit was filed on Monday in the 5th U.S. Circuit Court of Appeals in New Orleans on behalf of the trade group Airlines for America and certain carriers including American Airlines, Delta Air Lines, United Airlines, JetBlue Airways, Hawaiian Airlines, and Alaska Airlines.

Related: Delayed, Cancelled Flights Now Eligible for Full Cash Refund

The airlines are calling the new rule "an abuse of discretion" and claim that the agency is overstepping its power by going "beyond its authority" in an attempt to "regulate private business operations in a thriving marketplace."

The law, announced on April 24, requires airlines to disclose and explain all "surprise junk fees" upfront "clearly, conspicuously, and accurately" to passengers before they purchase their tickets.

Southwest Airlines did not join the lawsuit — the airline has never charged for checked baggage or charged fees for canceling or changing a flight.

"Overall, we support every airline's right to price its products but believe fees should be clearly and consistently disclosed so consumers can make informed purchasing decisions," Southwest said, per the Associated Press.

The USDOT claims the new law will save travelers over $500 million a year in fees.

"Airlines should compete with one another to secure passengers' business — not to see who can charge the most in surprise fees," Transportation Secretary Pete Buttigieg said at a press conference, at the time.

Related: Delta Airlines Is Increasing Checked Bag Fees This Week

"We will vigorously defend our rule protecting people from hidden junk fees and ensuring travelers can see the full price of a flight before they purchase a ticket. Many air travelers will be disappointed to learn that the airline lobby is suing to stop these common-sense protections," the department said Monday.

It's estimated that airlines made $33 billion in 2023 in checked bag fees alone.