The Postal Regulatory Commission approved higher nonprofit postage rates Thursday that charity magazine publishers say will impose onerous new financial burdens. The new rates take effect May 31.

Charities that send out letters and small pieces such as postcards, a category known as nonprofit standard mail, will pay about 2 percent more in postage under the new rates. However, publishers of well-known magazines such as Consumer Reports, Guideposts, andNational Wildlife will see much higher increases.

Guideposts, for example, will spend 8 percent more for postage, while its companion magazine, Angels on Earth, will cost more than 5 percent more to mail, said Jim Asselmeyer, the publisher’s vice president of operations. The two periodicals will cost an additional $420,000 more to mail per year, and the organization will spend another $140,000 annually on the standard mail it uses to promote the publications and recruit new subscribers.

Charity publishers fought hard to hold down the hike for nonprofit periodicals. It appeared they were making headway when the Postal Regulatory Commission sent the proposed rate increases back to the U.S. Postal Service twice — a move that experts said was unprecedented.

But in the end, the Postal Service made only minor adjustments to its initial rate proposal. For example, Consumer Reports and three related publications, which have 4.7 million subscribers, would have cost $1 million more annually to mail under the Postal Service’s initial proposal. Under the rates approved Thursday, the increase will be about $900,000, to about $13 million annually.

“I was hoping for something more meaningful,” said Meta Brophy, director of procurement services for Consumer Reports. “We just have to live with it.”