It's the first increase in postal rates since 2002, when the first-class rate went from 34 to 37 cents. But it may be followed by another rate hike next year.
In addition to 39 cents for a letter, postcards and additional ounces will increase from 23 to 24 cents. There are corresponding increases for other services as well.
"This rate increase that goes into effect on Sunday is 5.4 percent across the board," U.S. Postal Service spokesman Gerald McKiernan told CBSNews.com. "Every rate class that we have is being raised equally."
Local post offices should have plenty of new Statue of Liberty-and-Flag stamps, in all formats — sheets, rolls ("coils") and booklets. No denomination is printed on the new 39-cent stamps; a denominated version is expected next month.
In addition, the Postal Service has replenished its stock of two-cent Navajo Necklace stamps. Some post offices may also have sheets of a one-cent bird stamp or rolls of a one-cent Tiffany Lamp, so that customers can use up their 37-cent stamps.
The first 39-cent commemorative stamps are next week's Favorite Children's Book Animals, a set of eight that includes Curious George, the Very Hungry Caterpillar, and Maisy.
Other stamps to cover other rates as well as new stamped envelopes will be issued over the next several months.
Times have been good for the agency. The USPS "ended 2005 with a record sixth consecutive year of growth in productivity, wiped out its debt and delivered fifty percent more mail to 32 million more homes and businesses than it did 20 years ago," it declared in a press release last month.
So why what the Postal Service calls an "artificial" rate increase?
"The postal increase that goes into effect on Sunday really has nothing to do with postal expenses, such as salaries or the rising cost of fuel or maintenance of buildings. It has everything to do with fulfilling the obligations of an escrow account that Congress established in the year 2003," McKiernan said.
"But that $3.1 billion will not be used for postal operations," he added.