The American Civil Liberties Union has once again come to the defense of U.S. Sen. Larry Craig with a friend-of-the-court brief that argues police violated the constitutional rights of the Idaho Republican when he was arrested in a sex sting last summer.

In its brief, filed Tuesday with the Minnesota Court of Appeals, the ACLU argues that there's nothing illegal about soliciting private sex in a private place — in Craig's case, from an undercover police officer in a bathroom stall at the Minneapolis-St. Paul Airport.

Craig's actions were constitutionally protected free speech, the ACLU argues.

"Because the government may not criminalize private sex, it may not criminalize an invitation to have private sex," the ACLU brief says. "This is even so where the invitation is extended in a public place, whether a bar or a restroom."