Serena Williams’ recent U.S. Open outburst following accusations of cheating reportedly have several tennis umpires up in arms—The Times of London reports many are considering forming a union and boycotting matches featuring the 23-time Grand Slam singles winner.

Williams addressed umpire Carlos Ramos after he accused the athlete of cheating when she received hand signals from her coach. The Compton native vehemently denied any foul play, but Ramos penalized her a point anyway and then a game after the superstar broke her racket out of frustration. Williams called Ramos a “liar” and a “cheat,” and accused him of sexism.

The Women’s Tennis Association and the United States Tennis Association (USTA) have come out in support of Williams, to the chagrin of several umpires. One unidentified umpire told the Times that the USTA did not support umpires and that Ramos was  “thrown to the wolves for simply doing his job and was not willing to be abused for it.”

The International Tennis Federation, however, defended Ramos on Monday, saying his “decisions were in accordance with the relevant rules” and he “acted at all times with professionalism and integrity.”