The grounding of a UPS plane in Phoenix Tuesday night after two warnings of bombs in its cargo hold is fueling two lawmakers' push for better screening of cargo shipped by air.

Reps. Ed Markey (search), D-Mass., and Chris Shays (search), R-Conn., who met Wednesday with members of the Coalition of Airline Pilots Association (search), have been calling for more checks of air cargo.

House and Senate conferees were meeting Wednesday to go over the $29.4 billion Homeland Security budget for fiscal year 2004. The House version includes an amendment offered by Markey and Shays that demands the Transportation Security Administration (search) map out a plan for full inspections of all cargo on passenger planes.

The amendment forces Congress to divert federal funds away from any TSA cargo security plan that does not incorporate full screening of air cargo by the end of 2003. The 2004 fiscal year begins Oct. 1.

"While TSA employees are required to examine the booties on a baby's feet, no one is inspecting the boxes destined for the belly of a Boeing," Markey said earlier this month. "Is there any question where a bomb is likely to be placed?"

The Senate version of the Homeland Security spending bill does not include the Markey-Shays amendment. To encourage the inclusion of the amendment in the final bill, Markey, Shays and CAPA handed out the association's annual security report card, giving TSA low marks for airplane security.

CAPA gave cargo screening an F, and handed out a series of low grades for crew self-defense training, threat intelligence and other factors. It awarded scores of a B for luggage screening and a B for flight deck doors.

They regard the failure to screen and inspect cargo as a "gaping loophole in our passenger plane security system," Israel Klein, spokesman for Rep. Markey, said. "It’s a huge loophole that still exists. Knowing that Al Qaeda (search) intends to target airplanes, it is the one huge hole that homeland security hasn’t closed yet."

Shays and Markey face some formidable foes as the White House, and airline industry representatives have been lobbying against the measure. They say the high costs connected with the measure make it impractical. Cargo on passenger airlines amounts to one-fifth to one-third of revenue, and it has an even larger effect because profit margins are significantly higher for cargo than for passenger tickets.

Markey said the Bush administration's policy is "pennywise and pound foolish," but acknowledged the difficulty in passing this legislation.

"I'm not optimistic about what is going to happen in the Appropriations Committee," he said, adding that if the measure suffers a setback in committee, he and Shays will take the fight to the House floor.

"Safety cannot take a backseat . . . because putting safety in the backseat jeopardizes everyone in the passenger seat," Markey said.

Though no bomb was found on the 757 that made an emergency landing at Phoenix Sky Harbor International Airport on Tuesday night, the incident is a reminder of continuing threats to security.

Unlike passenger airlines, cargo carriers like UPS and Federal Express set their own rules for package screening, the guidelines of which are kept secret.

Captain Lee Collins, a security representative for CAPA, warned of the danger of a successful attack on air cargo, saying that the potential cost of failing to guarantee security is "huge."

He said an attack on air cargo could have a much worse economic effect than a hijacking because of the nationwide economic ripple effect on business and industry.

The plane, which had taken off from Los Angeles and was traveling to Louisville, Ky., with two crew members and a third UPS employee, had received two phone calls claiming a bomb was on board in a package. The caller gave the package's shipping number.

After members of Phoenix's bomb squad unloaded the grounded plane by hand early Wednesday, they uncovered a box containing bottled water, fabric softener and cabbage, said Jeanine L'Ecuyer, spokeswoman for Sky Harbor International Airport.

"This was a hoax," L'Ecuyer said.

Also responding to the incident were the Phoenix police and fire departments, members of the FBI, the Arizona Department of Public Safety and bomb-sniffing dogs.

Fox News' Kelley Beaucar Vlahos contributed to this report