Regulators rejected a request to make the price hike permanent. The change takes effect Jan. 26 and will last no more than two years, allowing the Postal Service to recoup $2.8 billion in losses.
The independent Postal Regulatory Commission said the change is justified by mail volume decreases since 2008.
Regulators said the Postal Service has to come up with a plan to phase out the higher rates once the lost revenue is recouped. It's unclear if that would take rates for first-class postage back to 46 cents in 2016 or to a different level.
Forever stamps, good for first-class postage whatever the rate, can be purchased at the lower price until Jan. 26.
Bulk mail, periodicals and package service rates will go up 6 percent.
The mail industry opposes the price increases. It says charities using mass mailings and bookstores competing with Amazon will suffer.
The Associated Press contributed to this report.