Four of the 10 Democratic presidential candidates who will take the stage Wednesday night for the fifth primary debate sent a letter to DNC chairman Tom Perez on Tuesday, demanding an independent investigation into what they call the “toxic culture” of sexual harassment at NBC.

The letter is signed by Sens. Cory Booker (D-NJ), Kamala Harris (D-CA), Bernie Sanders (I-VT) and Elizabeth Warren (D-MA). It does not call for cancellation of the debate.

Wednesday’s debate in Atlanta is being hosted by MSNBC and the Washington Post. The media giant Comcast is also involved as the owner of NBC Television.

“The letter comes following the release of a book by journalist Ronan Farrow, which details allegations of sexual harassment and assault within the network, including an allegation that former anchor Matt Lauer raped an NBC employee,” reports The Hill.

Lauer, who was fired after the rape allegation was reported, insists his sexual relations with the employee were consensual.

“After CBS News and Fox News faced similar allegations, both networks brought in outside law firms to investigate company culture,” says the Huffington Post. “In contrast, NBC went with company lawyers, releasing a report last year that largely cleared the network of any wrongdoing.”

The letter, says HuffPost, was “coordinated” by the women’s advocacy group UltraViolet.

In it, the four senators say they “are very concerned about the message it would send to sexual assault survivors if our next debate is sponsored by MSNBC without clear commitments from Comcast … to conduct an independent investigation into the toxic culture that enabled abusers and silenced survivors.”

NBC said in October that it “swiftly” took “appropriate actions to address the situation and improve workplace culture” at the network.

But earlier this month, Post media columnist Margaret Sullivan described the situation as she saw it:

“NBC has made a loud and clear statement about its values: Profits matter more than journalism, ratings more than truth.”