More than a dozen “One Tree Hill” crew and cast members, including Sophia Bush, Hilarie Burton and Danneel Harris, penned a letter on Monday accusing creator Mark Schwahn of “traumatizing” sexual harassment on the set of the show.

The 18 women, who previously worked on the popular TV drama, released the letter after Audrey Wauchope, a former writer on “One Tree Hill,” wrote in a series of tweets on Saturday detailing alleged harassment she and other women faced from Schwahn, who she only referred to as the “showrunner.” She claimed that Schwahn would show other men naked photos of an actress “he was having an affair with” and would touch female members inappropriately, including massaging shoulders, petting their hair and putting his arms around them.

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“He's a man in a position of power who was allowed to run a television show for years where this behavior continuously went on,” Wauchope tweeted. “I don't blame the men on that staff - I truly believe they were also in a way victims of psychological abuse and didn't know what to do.”

“I'm furious and sad and everything else for the women who have sat on that couch next to that man. And I'm furious and sad and everything else that years later I don't feel safe to be able to do anything real about this and that it seems to be happening all over this town,” she wrote.

In Monday’s letter, obtained by Variety, the women said “Schwahn’s behavior over the duration of the filming of 'One Tree Hill' was something of an ‘open secret.’”

“All of the female cast members of 'One Tree Hill' have chosen this forum to stand together in support of Audrey Wauchope and one another," the letter read.

They added, “Many of us were, to varying degrees, manipulated psychologically and emotionally. More than one of us is still in treatment for post-traumatic stress. Many of us were put in uncomfortable positions and had to swiftly learn to fight back, sometimes physically, because it was made clear to us that the supervisors in the room were not the protectors they were supposed to be.”

“Many of us were spoken to in ways that ran the spectrum from deeply upsetting, to traumatizing, to downright illegal. And a few of us were put in positions where we felt physically unsafe. More than one woman on our show had her career trajectory threatened,” they wrote.

The actresses and crew member said they confided in each other about Schwahn’s alleged sexual misconduct and warned new women who joined the series over the years. They claimed that everyone on set was fully aware of Schwahn’s actions.

“The lack of action that has been routine, the turning of the other cheek, is intolerable. We collectively want to echo the calls of women everywhere that vehemently demand change, in all industries,” they wrote.

The group said they were threatened that the series, which ran from 2003 to 2012, would be canceled if they came forward with the allegations and that “hundreds of lovely, qualified, hard-working, and talented people losing their jobs.” The threat placed pressure on young girls, they added.

“Many of us since have stayed silent publicly but had very open channels of communication in our friend group and in our industry, because we want Tree Hill to remain the place ‘where everything’s better and everything’s safe’ for our fans; some of whom have said that the show quite literally saved their lives. But the reality is, no space is safe when it has an underlying and infectious cancer,” the letter read. “We have worked at taking our power back, making the conventions our own, and relishing in the good memories. But there is more work to be done.”

The letter concluded, “We are all deeply grateful for Audrey’s courage. For one another. And for every male cast mate and crew member who has reached out to our group of women to offer their support these last few days. They echo the greater rallying cry that must lead us to change: Believe Women. We are all in this together.”

The letter was signed by Bush, Burton, Joy Lenz, Danneel Harris, Michaela McManus, Kate Voegele, Daphne Zuniga, India DeBeaufort, Bevin Prince, Jana Kramer, Shantel Van Santen and Allison Munn. Six members crew members also signed it, including Wauchope and Rachel Specter.

In a statement to Variety, E!, Universal Cable Productions and Lionsgate Television — the companies supporting Schwahn’s current show, “The Royals” — said: "We are monitoring the information carefully. E!, Universal Cable Productions and Lionsgate Television are committed to providing a safe working environment in which everyone is treated respectfully and professionally.”

Many of the former “One Tree Hill” actors, including Austin Nichols, James Lafferty and Stephen Colletti, tweeted on Tuesday in support of the actresses and crew members.

“I applaud every woman on 'OTH,' every woman on earth, who stands up to a system that has failed them in the past and in this moment. I stand with them,” Lafferty said in a statement.

Nichols said, “I stand with all my 'OTH' sisters. We have to change. We have to be better. All of us. This is unacceptable.”

“I have the utmost respect of your position in righting the wrongs you have endured,” Colletti tweeted. “I stand for you, for better...”