Some retirees could see sharply lower pension payments as a result; others will see little change in benefits, depending on a variety of factors. Some retirees at US Airways, which has terminated its plans, have seen benefits drop by as much as 50 percent.

The airline, which has been in bankruptcy protection since December 2002, has been pushing to end its pensions since losing its bid for a federal loan package last year. But unions representing United's employees fought the action, threatening to strike if the pensions were set aside.

Along with raising that prospect, the action has significant implications for the airline industry, which has lost more than $30 billion since 2000, and perhaps for other industries like automobiles, with similarly heavy legacy costs.

Analysts have predicted that if United won its case, there could be a domino effect as other airlines are forced to seek bankruptcy protection to bring their pension costs down to United's levels.

That move would probably swamp the pension agency, which was created in 1974.

"It's a scale, and this is another weight on the side of the scale that puts pressure on the other airlines to follow in United's footsteps," said Gary M. Ford, a lawyer specializing in pension and bankruptcy issues at the Groom Law Group who is representing some of the other large airlines. "The question is, Do you want to just watch this movie again, or is Congress going to act in a way that would make these plans affordable for the remaining carriers?"