Excerpt: The U.S. government told United Airlines on Monday that the nation's No. 2 airline is violating federal law by suspending $568 million in payments to its pension plans. 'The decision to stop contributing to the pension plans is a serious matter that increases the risk of loss to plan participants and the federal pension insurance program,' wrote Bradley Belt, executive director of the U.S. Pension Benefit Guaranty Corp., in a letter to United chief executive Glenn Tilton.