The beleaguered federal agency charged with insuring pensions has filed an objection to a deal struck between Delta Air Lines Inc. and its pilots.

The Pension Benefit Guaranty Corp. said in a filing made Wednesday at the U.S. Bankruptcy Court for the Southern District of New York in Manhattan that a provision in the deal between the airline and its pilots violates pension law. Specifically, the agency objects to a $650 million note promised to pilots to offset reductions in retirement benefits should the airline terminate its pension plans as expected.