Several Republican attorneys general are arguing that President Joe Biden’s COVID-19 vaccine mandate on private businesses is unenforceable because no rule has yet been issued by the Labor Department, adding they are prepared to challenge the rule in court the moment it is published.

“No such rule or regulation is currently in effect,” Montana Attorney General Austin Knudsen noted in an open letter to his state’s residents, and “there has been a great deal of confusion” since Biden made his announcement Sept. 9.