A prominent local attorney, who supported San Diego Mayor Bob Filner's 2012 campaign, is now asking Filner to resign.
Cory Briggs sent his request to Filner via a letter on Tuesday, saying if Filner remains mayor it will "cause long-term damage to the movement to clean up City Hall."
He said Filner has violated the principles of open, accountable and responsible government.
"Certainly you are entitled to broad latitude in your efforts to put the city back on a proper course, but that latitude is not limitless," Briggs wrote.
Briggs, who was listed as endorsing Filner on the mayor's campaign website, said he arrived at his decision "reluctantly."
Filner has come under fire recently for accepting a $100,000 donation from developer Sunroad Centrum Partners for a pair of municipal contracts.
Filner later returned the money after discovering that his second-highest aide at the time told the developer its donation would secure the mayor’s support for easing the restrictions on its Centrum 23 project in Kearny Mesa.
Briggs represents the group, San Diegans for Open Government, which just filed a lawsuit Wednesday over the Sunroad donation.
The group claims the city engaged in a "pay-to-play scheme" in violation of the City Charter, the city's municipal code and the California Environmental Quality Act (CEQA).
The litigation calls Sunroad's $100,000 donation a quid pro quo payment to get its project approved.
Last week, San Diegans for Open Government filed a lawsuit against San Diego City Attorney Jan Goldsmith, accusing Goldsmith of acting illegally by releasing a transcript of a closed-session meeting without obtaining permission from the City Council.
The transcript showed Filner ordering police to escort Deputy City Attorney Andrew Jones out of a closed-session meeting.