The Law is on Donahoe's Side Regarding Saturday Delivery
Postmaster General Patrick Donahoe confused both the news media and fuming Congress members today with his explanation of why Saturday mail service can be ended without Congressional approval. But he appears to be on solid ground legally. In fact, the case for the U.S. Postal Service making this move was laid out more than three years ago.
Congress still has the power to prevent the ending of Saturday delivery (for all but parcels) by passing legislation that specifically requires six-day delivery.