They might have done that already. I went in to what used to be a very busy P.O.the other day and joked how I could walk right up to the counter. I wanted to mail a small box that used to cost me about 5.00 to mail and they wanted 13.00 to mail it! That was more than UPS with insurance and real tracking. I ask about the cost and I was told rates went up 3 weeks ago, particularly for none local deliveries.
I use the Post Office almost daily to mail packages. The rates did go up from .05 to .25 cents. The rates are also affected by weight,size of package and Zones. A 1 lb package sent priority mail with delivery confirmation to Zone 2 Fresno is $5.95 while the exact same package sent to South Carolina Zone 8 costs $7.05
In the normal world prices are based upon supply and demand. If everyone wants your product you can raise your prices. In the case of the USPS, they have a product that no one really wants or even needs anymore so they defy the laws of economics and raise prices.
Government in action.