Facing abuse and anger over its decision to ban Manchester City, the English soccer champion, from its competitions, European soccer’s governing body this week took the unusual step of ordering its staff members not to wear branded clothing when they travel to matches involving the team, or even to games played in Manchester.

The warnings from the body, UEFA, included the Europa League match on Thursday between Manchester United and Club Brugge of Belgium.

Manchester City fans have fumed for years about what they consider the mistreatment of their club by UEFA. But that anger has increased since Feb. 14, when UEFA issued Manchester City a two-season ban from the Champions League, starting next season, and a fine of 30 million euros ($27 million) after an investigation into accusations that City had violated UEFA’s cost-control regulations.

The club’s response throughout the process has been a full-throated denial, and accusations that UEFA’s process has been biased and prejudicial. It filed its official appeal of the punishment on Wednesday at the Court of Arbitration for Sport in Switzerland.