O.V. Delle-Femine, national director of the Aircraft Mechanics Fraternal Association, said that interest is occurring on the deferred amount and putting pension plans at greater risk.

"If United is unable to make up the deferred payment with interest, this will cause major problems with the plans," Delle-Femine said after a meeting between union and airline executives.

United, a unit of UAL Corp., deferred its quarterly pension payment last week to give it more flexibility for managing resources as it tries to secure investors for bankruptcy exit financing.