The UH-1 Huey has been a mainstay of U.S. wars since its debut in the jungles of Vietnam. Now, the Air Force is looking to retire the venerable aircraft, and lawmakers are fighting over how it will be replaced.

The Air Force fields roughly 60 UH-1N Hueys that are split between a number of missions. One contingent of the helicopters provides security to intercontinental ballistic missile sites, while another is meant to evacuate members of the government during a time of national emergency. The Air Force also uses a small number of Hueys for search- and-rescue missions.

The Air Force has been eyeballing a replacement for the Huey since the early 1990s but steadily delayed making a decision until the service’s most recent attempt in 2013. The initiative, called the Common Vertical Lift Support Platform program, was cut out of the 2013 defense budget because of sequestration. The Air Force has since moved forward with an acquisition strategy to replace the Hueys after Strategic Command determined earlier this year that there was now an “urgent need” to replace the aging helicopter. The Marine Corps currently uses a more modernized version of the Huey and has no plans to replace it.

The Army, which first deployed Hueys in combat in Vietnam in the 1960s, phased out the UH-1 in favor of the UH-60 Black Hawk, retiring it from active Army service a decade ago.

“Right now the Air Force is looking at all options as we go forward to meet the need,” ” Air Force spokeswoman Ann Stefanek said, adding that one way the Air Force might replace the Huey is through something called the Economy Act.

The Economy Act of 1932 is an obscure law that allows for federal agencies to buy goods from other federal agencies if it is in the “best interest” of the government and if the goods “cannot be obtained as conveniently or economically by contracting directly with a private source.”

The Economy Act, along with another avenue the Air Force is exploring, known as a sole-source award, would allow the Air Force to replace the Huey without competition from outside vendors — an option that has garnered support from some lawmakers, while others are up in arms. Generally, government contracts are supposed to go through a rigorous bidding process between competing vendors before a contract is awarded.

In a letter sent in February to ranking members of the House Armed Services Committee and obtained by The Washington Post, 17 members of Congress urged that the committee add language to the upcoming 2017 National Defense Authorization Act mandating that the Air Force purchase UH-60 Black Hawk helicopters from the U.S. Army to replace the Huey.

“The failure to modernize these helicopters has created a glaring gap in the security of our nation’s nuclear weapons,” the letter reads. “By adding Black Hawks to the Army’s current block buy contract and directing the Air Force to purchase them, we can address the problem immediately.”

Seven of the letter’s signatories represent districts that deal directly with Lockheed Martin and Sikorsky, an aeronautics company headquartered in Connecticut that makes the Black Hawk and was purchased by Lockheed Martin in 2015 for $9 billion. In the last two years, Sikorsky has also won two helicopter contracts: one for the new Marine One, the presidential helicopter that lands on the South Lawn of the White House, and another for the Air Force’s combat search-and-rescue Black Hawks.

Black Hawk variants are widely used by other branches of the military. But some critics say they aren’t a suitable replacement for the Hueys since they are bigger, and there are other, less costly designs available that would meet the Air Force’s requirements.

In March, the National Taxpayers Union and Citizens Against Government Waste both sent letters to the House and Senate Armed Services committees railing against a sole-source acquisition to replace the Huey. Twelve congressmen sent an April 14 letter to the House Armed Services Committee, also obtained by The Post, urging that the committee write language into the upcoming defense act that would allow for “a fair and open” competition to replace the Air Force’s fleet of Hueys.

“It is our collective view that a terrible precedent would be set if services were allowed to justify sole-source acquisitions by citing a sense of urgency due in part to a failure to properly plan and execute against known requirements,” the letter reads.

Rep. Mac Thornberry (R-Tex.), chairman of the House Armed Services Committee, indicated that the upcoming National Defense Authorization Act will set aside money for the Air Force to replace the Hueys. But it will not tell the branch how to go about doing that.

“This is an urgent need,” said Thornberry. “These helicopters are around 40 years old, and I’m not very pleased it has [been] allowed to get to this situation.”

This post has been updated with comments from Rep. Thornberry and to reflect that the Combat Rescue helicopter contract awarded to Sikorsky was not sole-source.