Delta Air Lines passengers who redeem their miles for free flights will soon need to start paying a fee of at least $25.

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The fuel surcharge, which goes into effect for award tickets booked Aug. 15 and later, will be $25 for SkyMiles award travel in the United States and Canada.

For international award travel, the fuel surcharge will be $50. That includes trans-Pacific and trans-Atlantic flights, as well as flights to the Caribbean, Latin America, Puerto Rico and the U.S. Virgin Islands.

Delta SkyMiles program managing director Jeff Robertson said in a press release Friday that the rising cost of fuel is "causing considerable financial stress to Delta's business."

Delta spokesman Kent Landers said the move is important to help mitigate fuel price challenges the company faces. "Hopefully we'll have the opportunity to re-evaluate [the surcharge] if fuel prices subside," Landers said.

Delta also plans in the next 60 days to make changes to its tiered award program and "other key initiatives."

The announcement comes after recent moves by other airlines to add fees for what used to be free award tickets. US Airways will begin charging a $25 to $50 award processing fee Aug. 6, and American Airlines will begin charging a $5 processing fee for award reservations effective June 21. Other fees apply if customers book awards over the phone.