Bayern Munich's stars Mario Goetze, Mario Gomez and Jan Kirchhoff have all been fined a reported five-figure sum for wearing Nike clothing, which had not gone down well with club sponsor Adidas.
New-signings Goetze and Kirchoff both wore Nike T-shirts at Tuesday's press conference to officially unveil them, while Gomez was photographed wearing a Nike cap at training on Thursday.
All three players are privately sponsored by Nike, but under the terms of the club's contract with rivals Adidas, they must only wear clothing made by the German sports brand at official events.
Bayern's media director Markus Hoerwick confirmed the players have been fined, with the proceedings going to the victims of last month's flooding in south Germany.
For the last decade, Bayern have a contract with Adidas, which runs until 2020, and the German sportswear giants own a 9.4 percent stake in the Champions League winners, which is worth 77 million euros (US$100m, £65m).
European champions Bayern play their first competitive game under new coach Pep Guardiola on July 27 when they face Borussia Dortmund in the German Super Cup in a repeat of May's Champions League final.