By Daniel Wallis

(Reuters) - A regional U.S. federal appeals court ruled on Monday that pornographic movie actors in Los Angeles must wear condoms during sex scenes, upholding a lower court decision that was challenged by the adult film industry.

In 2012, voters in Los Angeles County approved a measure to require condom use during sex scenes in pornographic movies, as well as the regular testing of actors for sexually transmitted diseases.

Lawyers for the industry challenged the regulations in U.S. District Court, arguing that the condom requirement went against their clients' right to freedom of expression under the First Amendment of the U.S. Constitution.

Pornographic movie producers have said visible contraceptives put off some of their customers, because they reminded them of real-world worries such as pregnancy and disease.

A three-judge panel of the 9th U.S. Circuit Court of Appeals upheld the requirement on Monday, saying it was narrowly tailored to achieve the County's interest of reducing the rate of sexually transmitted infections while also leaving open "adequate alternative means of expression."

The panel said it agreed with the lower court that, whatever "unique message" the film makers might hope to convey by depicting condomless sex, it was unlikely that viewers of adult films would understand that message.

Likewise, the San Francisco-based appeals court said, mandates to test actors, and to require producers to complete a county-approved training course on blood-borne pathogens, served the goal of preventing sexually transmitted infections.

It noted that three adult film makers listed among the plaintiffs in the case already required performers to provide identification and to submit to tests at least once a month.

Much of the U.S. adult movie industry, which is worth an estimated $9 billion to $13 billion a year, is based in Los Angeles County. The AIDS Healthcare Foundation has said actors in pornographic films are 10 times more likely to contract a sexually transmitted disease than the general public.

(Reporting by Daniel Wallis in Denver; Editing by Mohammad Zargham)