Michael Higby, the site's operator who provided a copy of the letter, defended the posts, but said he has removed them while he studies his legal options.
"What we have done for now is remove all content related to Mike Gatto as we strategize internally," Higby said.
The website has covered Los Angeles and state politics for six years, Higby said, often with a "snarky, rough-and-tumble" tone.
"Mike Gatto likes to control his image very tightly and for a politician he has an incredibly thin skin," Higby said.
Despite several acerbic posts about Los Angeles Mayor Antonio Villaraigosa over the years, Higby said, "we have never ever had any complaint or concern from the mayor's office. In fact, they frequently send us information."
Gatto, who is running against Republican Sunder Ramani for the Nov. 2 election, said he recognized that seeking to stop the posts on Mayor Sam's Sister City was unusual, but added that the site crossed the line in items referencing his wife and mother.
"Tomorrow, they may say I was on the grassy knoll when John Kennedy was shot," Gatto said. "Facts mean nothing to them."
One of the Mayor Sam's Sister City articles points out Gatto registered the domain name dealsondrugs.net in 1999, suggesting he was seeking to get into the illicit drug trade.
Gatto said that from time to time he has obtained the rights to domain names on the chance that they will become valuable.
"People buy domain names that are generic, such as buyclothesonline.com. That is all I've ever done," he said.
Getting the stories removed from the site was an important step, he added.
"As long as they stop these meritless attacks on me and my family, then I am OK with that. If they start again, I will pursue them to the fullest extent of the law," he said.
Bob Hope curfew put on hold