A group of bondholders is planning to reject iHeartMedia Inc.’s latest effort to push out maturities in a setback to the biggest U.S. radio operator teetering under $21 billion in debt, Bloomberg News reported on Friday. Almost half the holders of $347 million of bonds coming due in just over a year have banded together to oppose the debt exchange offered by the company. The unsecured creditors intend to notify the company that they won’t take part in the bond swap that would deliver so-called priority-guarantee notes maturing in 2021 to the holders. The group is working with law firm Paul Weiss and plans to push for better terms. The latest discord presents another potential setback in the radio broadcaster’s attempt to address a mountain of borrowings heaped on it from a 2008 buyout by Bain Capital and Thomas H. Lee Partners. The debt-load has complicated Chief Executive Officer Bob Pittman’s attempt to win back audiences who have been lured away by online music-streaming providers such as Spotify.