The regulation, meant to encourage condom use as an effective tool in the fight against AIDS, has seen the number of pornography productions in free fall since its passage at the end of 2012.
During that year, 480 permits to film porn in the region were granted, only to plummet to 40 in 2013 and 20 so far in 2014, said nonprofit FilmL.A., which issues the go-aheads.
"We haven't produced a movie in LA County since Measure B was passed in November 2012," said Steven Hirsch, founder and co-chairman of pornography production company Vivid Entertainment, using the statute's technical name.
He emphasized that the county "is the only place where people are required to wear a condom" on a pornography set.
Hirsch believed that a system in place for years -- which requires actors to take an HIV test before taking on a porn role -- "worked extremely well."
If a test came back positive, the actor couldn't be in a film. During 10 years, not one person became infected from porn work, Hirsch said.
"The performers don't want to use condoms -- they feel safe and comfortable (without them). The fans don't want to see condoms," Hirsch said.
- 10,000 jobs involved -
The law is driving porn productions to nearby counties, other states like Nevada or even abroad, Hirsch said.
Moves have caused increased budgets for productions in a sector already hard-hit by the availability of free porn on the Internet, he said, adding that an appeal against the law has been filed in court.
Stuart Waldman, president of the Valley Industry and Commerce Association in San Fernando said pornography is "a huge industry" for his region.
Porn movies account for more than 10,000 jobs and close to $6 billion in income in the San Fernando Valley, he said.
While actors from X-rated films are known to have contracted HIV -- five cases were reported in September 2013 -- Waldman said the individuals likely contracted the disease off the movie set.
"These are people who are probably having unprotected, unsafe sex in their private lives," Waldman said.
Michael Weinstein, president of the nonprofit AIDS Healthcare Foundation, said the law is not just about preventing HIV and AIDS.
"There have been thousands of cases of STDs over last 10 years" in the industry, he said.
And he said he expected the measure to be upheld in court, even if it is already being flouted by people filming in Los Angeles illegally.
He noted that porn production company Wicked Pictures, pornography producer Axel Braun and others already took the leap and make all their actors use condoms.
And the threat of a production exodus to other countries doesn't faze the AIDS activist, who compared any flight abroad to similar scenarios in other industries.
"You can manufacture in unsafe conditions in Bangladesh, but that doesn't mean we do that here," he said.