In a legal effort to help a US senator, the American Civil Liberties Union (ACLU) is arguing that people who have sex in public toilets have an expectation of privacy.

Republican Senator Larry Craig is asking the Minnesota Court of Appeals to let him withdraw his guilty plea to disorderly conduct related to a bathroom sex sting at the Minneapolis airport last year.

Craig was arrested by an undercover police officer who said Craig tapped his feet and swiped his hand under a stall divider in a way that signalled he wanted sex. Craig has denied that, saying his actions were misconstrued.