ST. PAUL, Minn. (AP) - In an effort to help Idaho Sen. Larry Craig, the American Civil Liberties Union is arguing that people who have sex in public bathrooms have an expectation of privacy.

Craig is asking the Minnesota Court of Appeals to let him withdraw his guilty plea from a bathroom sex sting at the Minneapolis airport. The ACLU on Tuesday filed a brief supporting Craig's side.

The ACLU wrote that a Minnesota Supreme Court ruling 38 years ago found that people who have sex in closed stalls in public restrooms "have a reasonable expectation of privacy."

That means the state cannot prove Craig was inviting the undercover officer to have sex in public, the ACLU wrote.

The Republican senator pleaded guilty to disorderly conduct. He has said his foot and hand motions near the stall divider were misconstrued by the police officer who arrested him.

The ACLU argued that even if Craig was inviting the officer to have sex, that wouldn't be illegal.

"The government cannot prove beyond a reasonable doubt that Senator Craig was inviting the undercover officer to engage in anything other than sexual intimacy that would not have called attention to itself in a closed stall in the public restroom," the ACLU wrote in its brief.

The ACLU also pointed out that Craig was originally charged with interference with privacy. The ACLU said that was an admission by the state that people in the bathroom stall expect privacy.