The three-cent increase is the largest hike in more than a decade.
It was approved on Dec. 24 to keep up with inflation and recoup losses from the Great Recession. The U.S. Post Office has exhausted a $15 billion loan from taxpayers to make up for shortfalls.
The change 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.
The Associated Press contributed to this report.