A senior member of the main U.S. union that represents opera performers resigned on Monday, accusing the organization’s leadership of a cover-up in its investigation into accusations of sexual misconduct against singer Plácido Domingo, according to the Associated Press.

Samuel Schultz, vice president of the American Guild of Musical Artists, provided complete results of the union’s investigation to the AP, which he claimed the organization’s membership had planned to keep secret as part of an agreement with Domingo.

Domingo, who has been accused of sexual misconduct by more than 20 women, recently apologized for his actions but dialed back that apology last week as European opera houses consider whether to cancel his future appearances.

As previously reported, Schultz said the deal involved Domingo paying the union a $500,000 fine and issuing a negotiated public apology in exchange for the full investigation not being disclosed. The union claimed the money would have covered the cost of its investigation and funding sexual harassment training. Schultz called it hush money that did a disservice to the women who stepped forward.

“This is a quid pro quo — silence in exchange for money,” Schultz said in a resignation letter, which he sent to union president Raymond Menard and executive director Len Egert and later shared with the AP. “I found AGMA’s willingness to bury the details of the investigative report deeply betraying of the women who were sexually harassed by Domingo.”

Egert denied any cover-up, telling the AP that the investigation’s details were kept confidential to protect the identities of people who requested anonymity, and that the union’s leaders felt a settlement would avoid formal disciplinary charges against Domingo and an internal hearing.

“Regrettably, due to Mr. Schultz’s admitted breach of confidentiality, the witnesses will now need to determine whether or not they will testify at a disciplinary hearing to prove the charges against Mr. Domingo,” Egert said.

The union filed disciplinary charges against Domingo on Friday. His name was removed from the Washington National Opera’s young artist program “in light of recent developments,” the opera house announced Tuesday.