Image caption Vivid Entertainment is one of the porn industry's biggest companies

Two major US porn companies have taken legal action to try to overturn a law requiring porn actors in Los Angeles County to wear condoms.

Vivid Entertainment and Califa Productions say the measure violates the guarantee of free speech in the US constitution's First Amendment.

The law, known as Measure B, was approved by voters in November.

The measure was supported by the Aids Healthcare Foundation (AHF), which said it would shield actors from HIV.

"Overturning this law is something I feel very passionate about," Steven Hirsch, founder of the Vivid Entertainment, told AFP news agency.

"I believe the industry's current testing system works well," he added.

Porn actors Kayden Kross and Logan Pierce are joining the challenge against the law.

HIV scares

Measure B expanded to county level an ordinance which had already been passed in the city of Los Angeles, requiring condom use as a condition of receiving a filming permit there.

Mayor Antonio Villaraigosa signed that measure into law in January 2012.

Adult production companies have threatened to move out of California because of the requirement, but face legal difficulties.

A 1988 ruling by the California Supreme Court prevented producers from being prosecuted under anti-prostitution laws, and only one other state - New Hampshire - has a similar ruling.

Adult film productions in the LA area have been suspended in the past because of HIV scares.

Critics of the condom requirement say actors are regularly tested, and such a requirement would hurt business and push production studios underground.

"We found that a lot of viewers at home don't want to see condom porn," Keiran Lee, a British porn actor in Los Angeles, told BBC's Newsbeat in January last year.