The city says the deal will save millions.
Hundreds of union workers turned in their IDs and badges at the airport Friday.
The janitors walked out in solidarity after the last shift ended. Some were overcome by emotion.
The janitors, represented by the Service Employees International Union, are being replaced by non-union workers per a new contract the city says will save taxpayers money.
Some of the janitors are being re-hired as non-union workers at a lower wage.
The janitors and their union made a final appeal to Mayor Rahm Emanuel Thursday, gathering outside his North Side home. The mayor has held his ground, saying the new contract saves the city millions.
"There will be places where we agree to disagree. I have never lost my fight," Emanuel said.
Despite the demonstration outside his home, protests around City Hall this week and appeals from the labor leaders, the mayor's office says it will not rebid the contract with United Maintenance. The city says the deal saves taxpayers millions of dollars, and the non-union company has hired 100 of the current janitors. But the hundreds of other longtime O'Hare workers are out of luck.
"These workers have done nothing wrong. Friday, less than two weeks before Christmas they stand to lose their jobs, livelihoods, retirement security and dignity, all because of a public contract that rewards a low bidder who threatens to cut wages, hours and benefits," said Jorge Ramirez, Chicago Federation of Labor.
The new cleaning company says it its starting wage will be about $12 an hour and will offer benefits and a 401K.
Geneva Daniels, a custodian for nine years said she can't hold back her tears.
"It is still up in the air. say a lot of prayers," said Daniels. "it is hard. It is devastating."
"I was one of the lucky ones that did get hired with the new company, but I lost my friends. We have been working together for many, many years, and I feel really bad for them," said Luz Reyes.