People mailing a letter will pay a little more for a stamp.

A three-cent increase on the cost of a stamp through the United States Postal Service went into effect on Sunday. The new rate of a First-Class Mail Forever stamp went from 63 cents to 66 cents.

The USPS said the reason for the increase is operating expenses fueled by inflation continue to rise and the effects of a previously defective pricing model are still being felt.

“These price adjustments are needed to provide the Postal Service with much needed revenue to achieve the financial stability sought by its Delivering for America 10-year plan,” the USPS said on its website. “The prices of the U.S. Postal Service remain among the most affordable in the world.”

This is the second price increase on the stamp this year.

The price for 1-ounce metered mail increased to 63 cents, and the price to send a domestic postcard increased to 51 cents. A 1-ounce letter mailed to another country increases to $1.50. There will be no change to the single-piece letter and flat additional-ounce price, which remains at 24 cents. These price changes include the launch of USPS Ground Advantage service and USPS Ground Advantage Return service.

The Postal Service is also making adjustments for Special Services products including Certified Mail, Post Office Box rental fees, money order fees and the cost to purchase insurance when mailing an item.

The United States Postal Service is an independent federal establishment, mandated to be self-financing and to serve every American community through the affordable, reliable and secure delivery of mail and packages to nearly 165 million addresses six and often seven days a week.