Stung by what they perceive as a lack of institutional support for the chair umpire who gave Serena Williams a game penalty late in the U.S. Open women’s final, which set off a firestorm of criticism, other umpires are reportedly discussing the possibility of boycotting her matches. Top umpires are also considering the formation of a union, according to a report Tuesday, in part because they are not allowed to discuss specific matches.

Williams was free to speak her mind after losing, 6-2, 6-4, Saturday to Japan’s Naomi Osaka, and she accused chair umpire Carlos Ramos of sexism. He had given her a warning for coaching, then a point penalty for smashing her racket and, after she repeatedly expressed frustration, including calling him a “thief,” Ramos levied the game penalty for verbal abuse.

The 23-time Grand Slam singles winner, one away from tying Margaret Court’s record for women or men, claimed that Ramos would not have treated a male player in such a harsh manner. The CEO of the Women’s Tennis Association, Steve Simon, quickly issued a statement of support for Serena, saying Sunday that his organization “believes that there should be no difference in the standards of tolerance provided to the emotions expressed by men vs. women” and that it did “not believe that this was done last night.”