The USPS is losing money because of the Postal Accountability and Enhancement Act of 2006. It required USPS pension funding to change from a "pay as you go" model to a pre-paid model. The postal pension fund is over 80% funded for future obligations - unlike the Federal workers pension fund which is $7 TRILLION dollars underfunded.
http://www.businessinsider.com... [businessinsider.com]
The problem is compounded by decreasing snail mail usage.