Besides letters, this affects those who use first class parcels for mailing bombs and anyone using a DC number that doesn't get it free from using the online label generator.
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Mailing Services Prices Effective Monday, May 11, 2009
On May 11 the price for a 1-ounce First-Class Mail stamp will increase from 42¢ to 44¢. Prices for other mailing services — Standard Mail, Periodicals, Package Services (including Parcel Post), and Extra Services — will also change. The average increase by class of mail is at or below the rate of inflation as measured by the Consumer Price Index.
See Complete Price List (PDF):
http://pe.usps.com/PriceChange_May2009/PDF/PriceList/PriceList.pdf
Customers can use their Forever Stamps — regardless of when purchased — to mail 1-ounce letters after the price change, without the need for additional postage. Forever Stamps are widely available through Post Offices, commercial retail outlets such as grocery stores, and online.
Prices for mailing services will continue to adjust each May. Prices for most shipping services, including Express Mail and Priority Mail, were adjusted in January and will not change in May.
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http://www.usps.com/prices/pricechanges.htm?from=home_ftpromo&page=NewMay09Prices
Even though priority mail package rates aren't changing, the cost of the DC number is.
