(CNN) -- Embattled San Diego Mayor Bob Filner and his representatives were in a closed door mediation with representatives from the city on Monday, while volunteers hoping to oust the mayor continued to collect signatures for a possible recall.
The session, which began at 10 a.m. PT (1 p.m. ET) was still in progress Monday afternoon, said a source with direct knowledge of the meeting, which included San Diego City Council President Todd Gloria.
The source declined to say what exactly was under discussion. The mediation is the first known meeting of its kind between Filner and the city.
The session took place the same day Filner supporters held a "We Will Not Be Silent" rally outside City Hall.
One day earlier, protesters who want the mayor to step down marched on the same spot.
"There is no excuse for abuse, and there is no excuse for you to stay in power," attorney Gloria Allred told the crowd.
She attended Sunday's rally along with some of the women accusing Filner, including one of her clients, 67-year-old Peggy Shannon.
So far, 16 women have come forward to say that Filner acted inappropriately, with accusations ranging from one woman's claim that the mayor gave her "tush a pat," to another's assertion that he "put in me what I guess now is the famous headlock."
Filner's office has not responded to multiple CNN requests for comment.
Last month, he acknowledged he "failed to fully respect the women who work for me and with me" and that he was "embarrassed" by his actions. But he also said he will be vindicated by "a full presentation of the facts" and that he would not step down.
The outrage is overwhelming.
Roughly 81 percent of city residents want him to resign, according to a poll conducted by CNN affiliate KGTV. Another affilaite, KFMB, reported local radio hosts hired skywriters to spell out "Surrender Bob" over areas of the city last week.
Armed with clipboards and pens, volunteers hit the streets of San Diego over the weekend to begin collecting signatures for a recall effort. They need more than 101,000 signatures by September 26.
"We're going to be everywhere. We're going to be at sporting events. We're going to be at street fairs, arts shows -- you name it, we will be out there," Dave McCulloch, an organizer, told KFMB on Sunday.
Filner, 70, was elected mayor in 2012 after 20 years in Congress.
His accusers range from a singer at a campaign fundraiser to his former communications director, who called him unfit for office. Shannon was the latest person to accuse Filner.
"Every day that I went to work, I had butterflies in my stomach because I did not know what was going to happen the next time the mayor came by my desk," she told reporters last week.
"I have three sons, four grandsons and two great grandsons. As our mayor, you should be -- but are not -- a role model for any of them," Shannon said.
Filner has rebuffed calls to resign from all nine City Council members and from fellow Democrats, including California's two U.S. senators.
His supporters, which include some labor unions and Latinos, claim Filner is being denied due process, and the recall effort is orchestrated by those who oppose his political agenda.
The mayor entered a two-week intensive behavior therapy program July 29, but his attorney, James Payne, said he was able to complete the voluntary program August 10. He was expected to continue with outpatient treatment, Payne said.
"Mayor Filner is taking personal time this week and is unavailable for comment, and we do not have information as to when he will be available for comment," said last week's statement from Payne's office, adding that it was not able to comment on the recall effort or other allegations leveled against the mayor.
Filner is expected to return to work this week, but Payne did not immediately return a CNN e-mail asking exactly when he would be back in the office.
The city attorney's office has said it could seek as a "last resort" a restraining order -- saying Filner creates a hostile environment for women -- to prevent him from returning to work, the Los Angeles Times reported.
The city attorney's office did not return calls seeking comment.
Though the city chief of staff changed the locks on Filner's office, it was to preserve evidence rather than to keep him out, the city attorney's office has said.
CNN's Kyung Lah, Matt Smith and Eliott C. McLaughlin contributed to this report.