Former Councilwoman Donna Frye recently stepped down as the mayor's director of open government. Frye says she wasn't harassed, but she says she has credible evidence Filner harassed several women.
She sent a letter to the mayor asking him to step down immediately and asked the city council to schedule a special election to replace him.
"I did not make this request lightly. It is one of the hardest decisions I have ever made," said Frye. "However, there are community standards in our society that need to be upheld when those standards are not respected, and someone needs to say that."
Filner later admitted Thursday in a statement that he had mistreated women in his office and apologized for his behavior.
"I begin today by apologizing to you. I have diminished the office to which you elected me.
"The charges made at today's news conference are serious. When a friend like Donna Frye is compelled to call for my resignation, I'm clearly doing something wrong. I have reached into my heart and soul and realized I must and will change my behavior.
"As someone who has spent a lifetime fighting for equality for all people, I am embarrassed to admit that I have failed to fully respect the women who work for me and with me, and that at times I have intimidated them.
"It's a good thing that behavior that would have been tolerated in the past is being called out in this generation for what it is: inappropriate and wrong.
"I am also humbled to admit that I need help. I have begun to work with professionals to make changes in my behavior and approach. In addition, my staff and I will participate in sexual harassment training provided by the city. Please know that I fully understand that only I am the one that can make these changes.
"If my behavior doesn't change, I cannot succeed in leading our city.
"In the next few days, I will be reaching out to those who now work in the Mayor's Office or have previously worked for me -- both men and women -- to personally apologize for my behavior.
"I will also be announcing fundamental changes within the Mayor's Office designed to promote a new spirit of cooperation, respect and effectiveness."
No charges have been filed against Filner.