In 1970, the Post Office became the Postal Service, with rates set by the Postal Regulatory Commission, and some oversight by the Congress.

Does Congress approve postal rates?

So long as the postal service meets its statutory requirements, the Commission does not have authority to deny or amend the price proposals.

How are postage rates determined?

The weight of your mailpiece is an important factor in determining the postage price you pay. ... For First-Class Mail, shape and weight will determine the price. For Priority Mail, the price is a combination of weight, size, and how far the mailpiece is traveling.