Sen. Elizabeth Warren (D-Mass.) called on former New York Mayor Michael Bloomberg to release women who worked at his company from nondisclosure agreements they signed after making sexual harassment and sex discrimination allegations. The challenge, issued at Wednesday night’s Democratic presidential primary debate in Las Vegas, came as Warren hammered Bloomberg over the scores of allegations that have been made over the years.

“The mayor has to stand on his record, and what we need to know is exactly what is lurking out there,” Warren said. “Mr. Mayor, are you willing to release all those women from these nondisclosure agreements so we can hear their side of the story?”

Warren described Bloomberg as having “muzzled” women who signed nondisclosure agreements while working at his company. Bloomberg and Bloomberg LP have faced almost 40 lawsuits from 64 women in recent decades. In several heated exchanges, Bloomberg described his hiring practices as progressive on gender equality, but Warren was not satisfied.

“I hope you heard what his defense was: ‘I’ve been nice to some women.’ That just doesn’t cut it,” Warren said.

Warren continued pressing Bloomberg as he attempted to minimize the allegations against him and his company. When Bloomberg said there were “very few” nondisclosure agreements, Warren interjected, asking, “How many is that?”

Mario Tama via Getty Images Democratic presidential candidates Mike Bloomberg and Sen. Elizabeth Warren (D-Mass.) sparred over nondisclosure agreements at the Democratic presidential primary debate Wednesday in Las Vegas.

Bloomberg struggled to respond to Warren’s jabs, and his defense that “none of them accused me of doing anything other than maybe they didn’t like a joke I told” drew groans from the audience. Bloomberg also attempted to frame the NDAs as mutual agreements that neither party would want disclosed, prompting Warren to challenge Bloomberg to release any signatory who did want to speak about her case.

“If they wish to speak out and tell their side of their story, that’s OK with you? You’re releasing them on television tonight?” Warren said.

“This is not just a question of the mayor’s character. This is also a question about electability,” Warren added. “We are not going to beat Donald Trump with a man who has who-knows-how-many nondisclosure agreements and a drip, drip, drip of stories of women saying they have been harassed.”

Bloomberg ultimately declined to say he would release women from their NDAs, falling back on his explanation that the agreements “were made consensually.” Former Vice President Joe Biden added to the criticism of Bloomberg’s NDAs, telling the former mayor to “say yes” to allowing the women to speak.

Bloomberg’s use of NDAs and refusal to release women from these confidentiality agreements has been a campaign issue for weeks, as the former mayor has denied any wrongdoing and tried to dodge Warren’s criticism. On the debate stage Wednesday, however, Warren was placed next to Bloomberg and repeatedly went on the offensive.

Warren ripped into Bloomberg at the outset, describing him as “a billionaire who calls women fat broads and horse-faced lesbians,” while multiple candidates condemned the racially discriminatory police policy of stop-and-frisk, which he expanded as mayor.