A Los Angeles City Hall proposal to send "john letters" to the owners of cars seen in areas known for prostitution has drawn criticism from a California civil liberties group.

The City Council voted Wednesday to have the city attorney's office analyze the proposal to use license numbers to determine who owns the vehicles.

The letters would be written to discourage those who were soliciting prostitutes from returning to the area while posing no harm to those who were there for legitimate reasons, Councilwoman Nury Martinez said.

"If you aren't soliciting, you have no reason to worry about finding one of these letters in your mailbox," she said.

The collection of license plate data is opposed by the nonprofit Electronic Frontier Foundation, the Los Angeles Daily News reported (http://bit.ly/1R8w0Ns ).

The San Francisco-based foundation has an ongoing lawsuit against the Los Angeles Police Department and the Los Angeles County Sheriff's Department over the issue.

"What happens if you have legitimate reason to be in a neighborhood?" asked Dave Mass, an investigative researcher with foundation.

Some other cities have used "john letters" to combat prostitution. In some communities, residents are encouraged to jot down the license numbers of cars they see engaging in suspicious activity and provide it to police.

The "john letters" are typically written in a cordial tone and make it clear that police do not assume the owner of the vehicle was the person driving it.

"It is a common myth that prostitution is a 'victimless crime' or that it is 'an act between two consenting adults,'" one sample letter cited by the newspaper states. "Prostitution is a crime which is linked to drugs (use and sale), acts of violence toward prostitutes and their customers, and in the worst case, human trafficking in juveniles for the sex trade."

The letters also warn about potential exposure to sexually transmitted diseases.

Some business owners praised the proposal in Los Angeles.

"Let's say that letter comes in and your wife, your girlfriend or mother gets it," said Cindy Sower, a Sun Valley business owner who applauded the proposal. "Maybe it's a wake-up call."