Sen. Barbara Boxer, D-Calif., released an open letter to embattled San Diego Mayor Bob Filner on Friday, calling for his immediate resignation because of accusations of sexual impropriety that the senator said “have shaken me to my core.”

“I have already said publicly that you should resign your office as mayor because of the shocking revelations by many women about your behavior toward them,” Boxer wrote. “But now I must say this directly to you: Bob, you must resign because you have betrayed the trust of the women you have victimized, the San Diegans you represent and the people you have worked with throughout your decades in public life.”

Boxer joins fellow California Democrat Dianne Feinstein in calling for Filner, a former member of the House of Representatives, to resign. Filner has been accused of sexual harassment by approximately a dozen women.

Read the full Boxer letter after the jump.

Dear Bob,

We’ve known each other for a long time, and have worked together on many issues that are important to the people of San Diego – from creating jobs to protecting the environment to helping our veterans.

So I am speaking to you now on a personal and professional level, and asking you to step down as mayor and get the help you need as a private citizen.

I have already said publicly that you should resign your office as mayor because of the shocking revelations by many women about your behavior toward them.

But now I must say this directly to you: Bob, you must resign because you have betrayed the trust of the women you have victimized, the San Diegans you represent and the people you have worked with throughout your decades in public life.

I have worked for so many years to prevent and punish sexual violence and sexual harassment, wherever they occur. As we fight in the Senate to stand up for the men and women in our military who are survivors of sexual assault, I have heard their stories, seen the anguish in their faces, listened to them talk about the pain that will always be with them.  Let me be clear: The latest revelations regarding your behavior toward women recovering from sexual assault – women who desperately need our help – have shaken me to my core.

Bob, you have already hurt so many people. To avoid hurting your victims and the people of San Diego more than you already have, you should step down immediately

Sincerely,

Barbara