(AP) – Leaders of the Proposition 8 campaign to outlaw same-sex marriage in California made an offer to businesses that have given money to the state’s largest gay-rights group: Give us money or we’ll publicly identify you as opponents of traditional unions.

Supporters of same-sex marriage called the tactic “an attempt to extort people” and “a bit Mafioso.”

ProtectMarriage.com, the umbrella group behind a ballot initiative that would overturn this year’s California Supreme Court decision legalizing same-sex marriage, targeted about 35 companies in the appeal, spokeswoman Sonya Eddings Brown said.

She called the letter “a frustrated response” to the intimidation felt by Proposition 8 supporters, who have had their lawn signs stolen and property vandalized in the closing days of the increasingly heated campaign.

Certified letters from the group last week asked companies to withdraw their support of Equality California, a nonprofit organization helping to lead the campaign against Proposition 8.

“Make a donation of a like amount to ProtectMarriage.com which will help us correct this error,” reads the letter. “Were you to elect not to donate comparably, it would be a clear indication that you are in opposition to traditional marriage. ... The names of any companies and organizations that choose not to donate in like manner to ProtectMarriage.com but have given to Equality California will be published.”

The letter was signed by four members of the group’s executive committee: campaign chairman Ron Prentice; Edward Dolejsi, executive director of the California Catholic Conference; Mark Jansson, a member of The Church of Jesus Christ of Latter-day Saints; and Andrew Pugno, a lawyer for ProtectMarriage.com.

A donation form was attached. The letter did not say where the names would be published.

San Diego business owner Jim Abbott, who is also a member of Equality California’s board of directors, received one of the letters on Oct. 22. Abbott’s adult son phoned and read the letter to him.

“He characterized it as a bit Mafioso,” said the managing partner of Abbott & Associates/Abbott Realty Group.

“It was a little distressing, but it’s consistent with how the ‘yes’ side of this campaign has been run, which is a bit over the top.”

Abbott, who married his same-sex partner at the end of August, estimated that during the last decade he has given $50,000 to Equality California, including a recent $10,000 gift to underwrite a San Diego event that raised money to defeat Proposition 8.

When asked whether ProtectMarriage.com planned to name businesses that have supported the “No on 8” campaign, Prentice initially said he was unaware of any such effort.

“I’m not familiar of any organized attack against organizations that have given to ‘No on 8’,” he said Thursday, the day after Abbott received his letter.

But when asked about the letter to Equality California donors, Prentice confirmed they were authentic and said the ProtectMarriage.com campaign was asking businesses backing the other side “to reconsider taking a position on a moral issue in California.”

Prentice said it was his understanding that the letter was intended for large corporations such as cable operators Time Warner and Comcast instead of small business owners like Abbott. Time Warner and Comcast are listed on Equality California’s Web site as corporate sponsors that gave $50,000 each to the group.

Companies that have contributed directly to one of the campaign committees collecting cash to fight Proposition 8, including one set up by Equality California, also were recipients of the letter, Prentice said. That list includes companies such as Pacific Gas & Electric, Levi Strauss and AT&T.

“I think the IDing of, or outing of, any company is very secondary to the question of why especially a public corporation would choose to take a side knowing it would splinter its own clientele,” he said.

Equality California executive director Geoffrey Kors said he has heard from two other business owners besides Abbott.

“It’s truly an outrageous attempt to extort people,” Kors said.

While an anti-Proposition 8 group called Californians Against Hate has posted lists of same-sex marriage ban donors on the Internet and even launched boycotts of selected businesses, Kors said that work has been independent of the official “No on 8” campaign.

“They are going after our long-term funding and trying to intimidate Equality California donors from giving any more to the ‘No on 8’ campaign and from giving to Equality California ever again, which would impact our work for seniors, youth and other people in need,” Kors said.

Opponents of the marriage ban say using threats to raise money reveals the true agenda of Proposition 8 supporters: to permanently harm the GLBT community, as well as its organizations, allies and supporters.

“If lies don’t work, then maybe threats and blackmail will,” said Delores Jacobs, CEO of the Center Advocacy Project. “That’s how low the other side is willing to go.”

But it hasn’t stopped at threats and blackmail.

Police say there are reports of both Proposition 8 supporters and opponents targeting each other with threats in verbal altercations, as well as defacing property and removing signs.

Stuart Schwartz, who lives in Kensington with his partner Jorge Schafer, have been the victims of such incidents on more than one occasion in the past few months.

The couple’s “No on 8” yard sign has been stolen, defaced or destroyed four times. Once somebody placed a “Yes on 8” bumper sticker over the “No on 8” decal on Schafer’s car. Most recently the couple’s “No on 8” sign was shredded and placed back in their yard and the words “God’s Law Yes On 8” written on their driveway in chalk. A sign which read the same was placed in a nearby bush.

“We both feel disturbed by the fact that people are not respecting our right to free speech,” said Schwartz, who noted he’s glad he only had to scrub chalk from the pavement.

Officials gave advice to place signage where it cannot be reached by perpetrators and to tightly secure them so they cannot easily be removed, he said. “However my partner and I took a different approach. We bring the sign in every night and put it back out again in the morning.”

While it can get worse the couple said they are not letting such bullying deter them from taking a stand against the ballot initiative.

“In any other circumstance I would characterize these despicable strategies as sad – but we are in the fight of lives here in California,” Jacobs said.

Supporters on both sides of Proposition 8 initiative, however, have been targets of such attacks.

Police say a 28-year-old woman was arrested for allegedly stealing “Yes on 8” campaign signs in Carlsbad last week.

Officers arrested Kimberly Erlenwein on Oct. 23 after they were told signs were being stolen from the center median of Carlsbad Village Drive. Police say 11 campaign signs in favor of Proposition 8 were found in her vehicle.

Erlenwein was cited and released.

The signs were photographed and returned to a “Yes on 8” representative.