Stockton Police Officers' Association spokesman Lee Neves said the allegations are "more than just a black eye" for the city.
"This is a devastating body blow," he said. "Given what has gone on over the past two weeks, he's just not able to effectively govern or represent the city anymore."
This is the latest scandal for the self-declared champion of children whose government website describes him as a Stockton native and single father who "has a passion for helping youth."
The charges came a week after The Record of Stockton reported that a gun stolen from Silva's home during a burglary was linked to the killing of 13-year-old Rayshawn Harris in Stockton early last year. The mayor is accused of not reporting the gun as missing until a month after the boy was killed.
Silva, who is seeking re-election in the fall, said the timing of the news about the gun was "politically motivated and calculated."
"I've never seen the victim of a theft be trashed in the media like I have," he said.
In a statement, the union said Silva has had "misstep after misstep" that he has "shrugged off" since he was elected mayor in 2012.
An affidavit by a San Joaquin County investigator does not identify the two females and three males it says were playing strip poker in the mayor's bedroom in August 2015.
An unnamed 18-year-old female told the investigator that all the participants in the game were naked at some point. She also said there was beer and vodka at the camp that hosts 75 children, according to the affidavit.
Silva posted $20,000 bail and was released from jail a few hours after his arrest on Thursday.
The charges stem from an FBI search of his cellphone last year, after he was stopped briefly at San Francisco International Airport by authorities who confiscated his laptop and cellphone as part of an unspecified investigation.
The FBI turned over contents of the cellphone to Amador County on July 26.
The contents included nearly two dozen photographs of people who appeared to be under 21 in possession of alcohol or near alcohol, said Amador County District Attorney Todd Riebe.
Riebe said one of four video recordings found on Silva's cellphone was of the strip poker game. The video contains mostly audio after players in the room said they didn't want to be video recorded, Riebe said.
Silva, a Republican, is running for re-election to lead the city of 300,000 people in the Central Valley. His opponent, Michael Tubbs, received more votes in the primary election and is endorsed by the police officers union.
Last year, Stockton emerged from bankruptcy protection by designing a plan to eliminate more than $2 billion in long-term debt payments without touching the city's pension obligations.