The U.S. Postal Service has recorded its first revenue increase in five years, but the agency still lost $5 billion in fiscal 2013, making it the seventh consecutive year of red ink.

The continued losses dampened the good news about increases and was compounded by the possibility that Congress will not pass legislation this year to help stanch the bleeding — which would make it the third straight year lawmakers failed to agree on a way forward to aid the struggling mail service.

The net loss for 2013 is largely the result of a requirement by Congress that the Postal Service pre-fund retiree benefits. The agency defaulted on its $5.6 billion prepayment last month.

Sen. Bernard Sanders, who has proposed legislation to end the obligation, said the Postal Service would have recorded a net profit of $600 million without the annual payment.