Flight attendants were walking from terminal to terminal to enlist grass-roots support, urging passengers to petition the White House.
It's the latest in a campaign to overturn a Transportation Security Administration decision that would allow flyers to carry small knives. The ban was imposed after September 11, 2001. The TSA plans to lift the ban on April 25.
"It is not only foolish, it is dangerous," said Dante Harris, president of the Association of Flight Attendants.
The flight attendants were joined by local members of Congress and five labor unions who say the change would cause longer security lines and increase potential hazards for everyone on a plane.
One pilot says a friend was flying a 9-11 jetliner that was hijacked and crashed.
"That day happened because knives were allowed on airplanes," said Scott Freeman, Air Line Pilots Association.
In a statement, the TSA said lifting the ban will improve efficiency: "This is part of an overall Risk-Based Security approach, which allows Transportation Security Officers to better focus their efforts on finding higher threat items such as explosives."
But one man said allowing knives could give passengers a fighting chance against a terrorist.
"If there was a terrorist on board and everybody had knives, we'd have a chance. Everybody would be armed," said Diamond Bar resident Bert Perez.
The proposed restriction is very specific: no blade longer than 2.36 inches. Critics say that just raises more questions.
"Won't that mean more needless work for the screeners while transportation security officers supposedly inspect each knife to see if it exceeds the maximum size?" asked U.S. Rep. Maxine Waters (D-Los Angeles).
As the unions apply more pressure, some members of Congress threaten to impose a restriction of their own: a law to overturn the lifting of the TSA ban.