CHICAGO (AP) -- Matt Hewitt flies at least once a week for work, and he usually travels on United Airlines because its routes are the most convenient for him.
But with three of the carrier's unions threatening to strike, Hewitt said he's is concerned about booking flights and taking advantage of the bonuses he's accumulated.
''I'm spending all my frequent flyer miles as soon as possible,'' Hewitt, a salesman, said Thursday after flying to Chicago from Sacramento, Calif.
Threats of strikes, while rarely carried out, are powerful bargaining chips in the airline industry. The hint of a strike can be costly in terms of lost bookings. If workers walk for any length of time, they can even put carriers out of business.
While trying to emerge from bankruptcy, United - the nation's second-largest airline - is seeking approval to replace existing contracts with mechanics and machinists with its own lower-cost versions.
And the flight attendants' union has threatened to strike over the latest round of labor givebacks, particularly the elimination of traditional pensions.
United is based in Elk Grove Village, near Chicago's O'Hare International Airport, where Franca Bukowski, a retired social worker from DeKalb, was waiting Thursday to accompany her husband on a business trip to Boston.
''It had no effect today, but we are worried once we get there that we'll be able to get back,'' she said.
Travel agents said there hasn't been any groundswell of concern expressed by their customers, nor do they expect any, unless the unions actually strike or if workers begin to disrupt operations in less organized ways.
At Carlson Wagon Travel Inc., the world's second-largest agency behind American Express, managers who handle corporate accounts said clients are booking trips on United as usual, according to spokeswoman Laurie Alexander.
''For now, they're monitoring the situation and don't feel the need to make any abrupt changes,'' Alexander said. ''We have contingency plans in place in case there is a strike.''
Richard Copland of Hillside Travel in New York said travelers have become somewhat inured to bad news coming out of the airline industry.
That was a sentiment evident in the dry humor of Paul Cummings, a manufacturing company manager, as he waited at O'Hare to check in for a flight to Toronto.
''United is my bankrupt airline of choice,'' he said. ''Until such time as they stop flying, I'll probably stay with them.''
AP Business Writer Brad Foss in Washington contributed to this report.