It was the second suspension of filming in less than three weeks. The first, week-long moratorium came in late August after Cameron Bay, an actress, tested positive for the virus.

Although industry executives have said the virus has not been transmitted on a film set, news of the HIV infections - the largest known outbreak in the industry since 2004 - has prompted renewed calls from activists to require condoms to be worn by pornographic performers.

Last year, Los Angeles County voters approved a ban on the production of sex films in which performers do not use condoms, though advocates for the law said it has not been strictly enforced.

But efforts to enact a similar ban across California, where most of the country's pornographic movies are made, have stalled in the state's Legislature.

"How many more people have to become infected? How many outbreaks do we need before it's clear that testing is not prevention?" asked Michael Weinstein, president of the Aids Healthcare Foundation, which campaigned to require condoms on sets of pornographic films in Los Angeles.

Weinstein said a fourth person connected to the pornographic film industry, who said he tested positive for HIV, had approached the organisation last week. In a statement, the Free Speech Coalition said it had no evidence that a fourth performer tested positive and accused Weinstein of political posturing.

Historically, the industry has been left to police itself and production companies, along with many performers, have opposed condom requirements.

"In the past eight years, nobody has contracted or transmitted HIV on set in the adult industry, and it's as a result of our testing procedures," said Steven Hirsch, the founder of Vivid Entertainment.

The Free Speech Coalition, which tracks test results for the industry, called for a moratorium on all filming nationwide after Bay reported testing positive for HIV last month. A week later, the group said all of her on-screen partners had tested negative, and lifted the moratorium.

But last Tuesday, another actor, Rod Daily, announced in a Twitter message that he too had tested positive for the virus.

Though he has performed mostly in gay films with condoms - condom use is more prevalent in gay pornographic films than in straight ones - he had been romantically linked with Bay.

Daily was tested at a clinic not affiliated with the industry.

As a result, the Free Speech Coalition did not call for another moratorium on filming or an investigation about whether his infection could have occurred on set, said Joanne Cachapero, a spokeswoman for the group.

"We asked him to come forward to us," she said, "but he has no obligation to do that."

But after a third performer tested positive for HIV, the coalition renewed the filming moratorium on Friday.