HELENA, Mont. (AP) — The Montana Broadcasters Association is cancelling a U.S. Senate race debate scheduled for Sunday morning in Whitefish.

The organization is citing "scheduling complications" that prevented Republican U.S. Rep. Denny Rehberg from attending.

Incumbent U.S. Sen. Jon Tester and Libertarian candidate Dan Cox of Hamilton were originally scheduled to debate without Rehberg. But the broadcasters announced Wednesday evening that they have cancelled the event since all three candidates cannot attend.

The Tester campaign is accusing Rehberg of breaking his word by backing out, arguing he is afraid to debate Tester. Rehberg's campaign blames organizers for failing to send a timely invitation.

It would have been the second debate, following a Saturday event in Big Sky. The candidates say they are working on plans for a Sept. 5 debate in Butte.