Four of the United States’ five largest airlines are squaring off in a debate roiling the domestic aviation industry over the regulation of so-called public charter flights.

The issue has come to a head over the rapid growth of charter operators like Dallas-based JSX that compete with regularly scheduled flights from smaller, private terminals without long security and boarding lines. That growth triggered a federal review of the regulations governing those operators.

American Airlines Group Inc. and Southwest Airlines Co. support cracking down on safety and security standards, closing a “loophole” being used by JSX and others, while United Airlines Holdings Inc. and JetBlue Airways Corp. — which each own a stake in JSX — argue for keeping the status quo, since these carriers provide service to small communities and a pipeline for pilots.

JSX markets itself as “the ultimate travel hack” that lets flyers “ditch the traditional airport route and arrive at our crowd-free terminals just 20 minutes before takeoff.”

The carrier does its own passenger screening it says is approved by the Transportation Security Administration. It can also hire pilots who don’t have the minimum 1,500 flying hours required for large scheduled carriers, and ones who are older than 65, the mandatory retirement age at such airlines.

Critics say the charter operator are taking advantage of what they characterize as a regulatory loophole that lets them make scheduled flights under a less-stringent set of safety and security standards.

The Federal Aviation Administration launched a formal review in August, saying the expansion of such carriers is “an increased risk to safety if left unchecked.”

Airlines, unions, airports, cities and travelers weighed in on the matter during a public comment period that closed Oct. 13.

The FAA and TSA have not specified when their assessments will conclude or what steps they might take.

At stake is revenue from business travelers who often book late and pay higher fares, and well-heeled leisure passengers seeking to avoid airport crowds. The push for changes is “pure back-room politicking done by competitors out of complete self-interest,” JSX Chief Executive Officer Alex Wilcox has said.

“It ultimately becomes a competitive issue if they’re successful,” Robert Mann, president of aviation consultancy RW Mann & Co. said of carriers like JSX. “They will claim more of these customers, and these are more of the high-value customers.”