Multiple reports say tensions between Madonna and Justin Bieber are developing backstage ahead of their planned performance at the World Cup halftime show at MetLife Stadium in New Jersey. The accounts describe an in-progress dispute involving the two headliners and note that concerns are being raised about how the situation could affect the run-up to the show. The sources characterize the issue as related to competing demands and heightened egos, suggesting it could escalate with hours remaining before the performance. They describe the halftime show as a high-profile event with a lineup intended to deliver a major spectacle, but frame the backstage environment as strained rather than settled. Neither set of reports provides independent confirmation from event organizers in the excerpts provided, and details about the specific nature of the disagreements are limited. The coverage nonetheless aligns on the core point: the planned halftime appearance proceeds amid reported backstage friction between Madonna and Bieber, with potential implications for coordination and show logistics.