The airlines may be running out of time.

For a couple of years, the industry's lobbying clout in Washington has kept Congress from adopting legislation that would require carriers to do more to ease their customers' pain from long airport tarmac delays.

Delays like the six-hour overnight ordeal endured by 47 passengers on a Continental Express regional jet flight at Rochester, Minn., last month.

Since that widely reported event, support has been building throughout the travel industry for legislation establishing a passenger bill of rights in federal law.

Tomorrow morning, proponents of the legislation will try to keep the momentum for passage going by staging their own version of a congressional hearing, taking testimony on Capitol Hill from supporters and opponents of the legislation.

Organizers of the hearing are the Business Travel Coalition - the Radnor advocacy group for corporate travel managers - and FlyersRights.org, formed by Kate Hanni, one of the victims of a nine-hour tarmac stranding in 2006.

The lineup of witnesses scheduled to appear tomorrow is impressive, and it includes both outspoken proponents of regulation and some who will speak against a legislative solution to the problem.

Among the invited speakers are Sens. Barbara Boxer (D., Calif.) and Olympia Snowe (R., Maine), cosponsors of a passenger-rights bill; retired American Airlines chief executive officer Robert L. Crandall and another former American official; executives from the Lehigh Valley and Dallas/Fort Worth airports; a leader of the American Society of Travel Agents; and a University of Michigan business professor who is against the legislation.

The senators' proposal, which has been approved by the Senate Commerce Committee, would require airlines to provide passengers with adequate food, water, usable restrooms, and necessary medical attention during long delays.

The key provision in the bill, the one the airlines don't like, would require that passengers be allowed to get off the plane after three hours, with a couple of 30-minute extensions if the captain determines there is a good chance the flight will actually depart.

The three-hour rule would also apply to flights stranded on an airport tarmac after landing because there are no available gates, a problem that can arise when thunderstorms keep planes from departing.

The U.S. House has already passed a weaker bill, but the leaders of this movement are opposed to it because it gives airlines too much leeway in deciding how long they keep passengers on planes.

The proponents of tougher regulation say they expect whatever bill is ultimately approved will be part of legislation reauthorizing the Federal Aviation Administration.

The airlines, represented by the Air Transport Association, have managed to fend off the legislative efforts in the past by arguing that hard-and-fast rules will have unintended consequences travelers won't like.

If your departing flight has to return to the terminal in three hours, it will lose its place in line to take off, meaning either the delay will get even longer or the flight will be canceled. With flights more than 80 percent full these days, finding a seat on another one will be tough, making it unpredictable when you'll reach your destination.

Airlines point out that federal safety regulations already prohibit them from doing anything on airport runways or ramps if thunderstorms, accompanied by lightning, are preventing takeoffs or jamming up gates.

What's more, the airlines say, only a tiny fraction of all flights experience ground delays of three hours or more, so what's the big deal?

But what has changed for the airlines since the Continental Express incident is the array of organizations and individual travelers now saying they don't care a whit how rare the problem is.

The National Business Travel Association and the American Society of Travel Agents in the last month have joined the Business Travel Coalition and FlyersRights.org in support of legislation as the only way to make the airlines behave consistently.

A survey conducted by the travel coalition of industry professionals and airline customers found that 82 percent were in favor of setting standards for how passengers should be treated during long delays, coalition chairman Kevin Mitchell said.

In the past, Mitchell agreed with the airlines' argument that setting a time limit on delays would be counterproductive because of the disruption it could cause for flight schedules. He testified against legislation at congressional hearings four times since 1999, when Congress first considered setting time limits.

Tougher rules were under consideration then because of another notorious incident, at the Detroit airport, where a snowstorm stranded thousands of Northwest Airlines passengers overnight.

The airlines persuaded Congress then to back off passing regulations by promising to adhere to voluntary customer-service plans.

Mitchell said that each time he testified, he warned the airlines that travelers and the rest of the travel industry would eventually lose patience if the industry didn't live up to its voluntary commitments.

"I thought the airlines should be given a chance to fix this problem," he said. "But 10 years is a long time of broken promises by the airlines that they would fix it."

Contact Tom Belden at 215-854-2454 or tbelden@phillynews.com.