The Femme Fatale tour is fully underway, but a new report says that co-headliners Britney Spears and Nicki Minaj are butting heads on the North American run, which just kicked off on June 17.

According to MediaTakeOut.com, a "trusted source" says, "[Britney] is upset that Nicki kept running over [her allotted] time. In Sacramento she was over about 10 minutes. But [on Saturday night in San Jose] Nicki went over by nearly 45 minutes."

Spears reportedly confronted the 'Super Bass' singer and her crew. "Britney came by Nicki's dressing room with her dancers," the insider added. "They were talking sh-- like they were going to do something. Nicki came out [of her dressing room] and at first was going to beat someone's a--. But when she saw how ridiculous Britney and them looked, she just laughed."

Whether real tensions exist has yet to be confirmed from either singer's camp, but with nearly two more months left on the extensive tour, it would be in the pop princess and rap superstar's best interest to play nice. The Femme Fatale tour will hit Las Vegas on June 25, and wrap on Aug. 13 in Toronto.

Watch Nicki Minaj Perform 'Fly,' 'Raining Men,' and 'Muny' on the Femme Fatale Tour