The U.S. Postal Service plans to stop delivering letters and other first-class mail on Saturdays, beginning August 1, although packages will continue to be delivered. Tired of waiting for Congress to help, the Postal Service later today is expected to unveil a series of more drastic cuts it plans to pursue that will save billions of dollars, a representative for the service said. It's unclear at the moment how the Postal Service has the authority to quit delivering letters on Saturdays. Previously, it has said it needed Congress to change the current law to do so. However, two sources confirmed to CNN that the plan includes an end to Saturday mail service except for package delivery, which has seen growth in the past few years.