United Airlines said it would not contribute to its employee pension plans while it remains under bankruptcy protection. That move could save it more than a billion dollars in cash over the coming year, but pension experts said it signaled the likelihood that United would terminate some or all of the plans.

A full-blown default by United on all four of its pension plans would send tens of thousands of current and future retirees, and billions of dollars in unfunded obligations, to the government’s pension insurance program, dealing the program its biggest blow since the government began insuring pensions in 1974