The U.S. Postal Service, which predicts that by the end of September it will be unable to make health-benefit payments for future retirees, said its first- quarter loss widened as first class mail volumes declined.

The loss increased to $329 million in the three months ended Dec. 31 from $297 million a year earlier, the Postal Service said in a statement today. Revenue fell 3.3 percent to $15.3 billion.