Washington • Sen. Mike Lee, R-Utah, cited free speech concerns in objecting Tuesday to legislation that would prohibit publishing blueprints to make 3D plastic guns.

Sen. Bill Nelson, D-Fla., attempted to pass a bill Tuesday by unanimous consent — meaning the measure would be approved unless any senator disagreed — that would ban anyone from posting online plans to use a 3D plastic printer to build a working firearm.

The move came as a deadline approached that night that would overturn an Obama-era ban on publishing the 3D gun plans. Plastic guns are undetectable by metal detectors at secure buildings and airports.

President Donald Trump's State Department reversed the publishing ban.

“Tonight at midnight," Nelson warned, “American national security is going to be ... irreversibly weakened because of the actions of the administration.”

Lee blocked the measure’s passage, saying he hadn’t had enough time to review it and saw constitutional concerns.

“Any legislation that comes forth from this body that begins with the following words will attract my attention and should attract the attention of anyone who’s concerned about our First Amendment and other constitutional rights,” the Utah Republican said on the Senate floor. “It begins with the words ‘it shall be unlawful for any person to intentionally publish.’ That ought to be concerning to us, to each and every one of us, Democrats and Republicans alike. On that basis, I object.”

Nelson countered that the government already restricts some speech, and courts have found that doesn’t violate First Amendment rights.

“There are many limits on our First Amendment rights of speech. You cannot say ‘fire’ in a crowded theater,” Nelson said. “Why in the world would you assert First Amendment rights to publish instructions to [make] a plastic gun that someone could take through a metal detector into a crowded theater and start shooting in that theater instead of shouting ‘fire,’ which is clearly an understood limitation upon our First Amendment rights of speech.”

Lee said the legislation wasn’t needed because possessing a firearm that can evade metal detectors is already illegal. He also noted that one can find books on making guns on the internet right now.

“This is a First Amendment issue,” Lee said in a statement. “When you are talking about banning the publication of instructions to do something, rather than banning the thing itself, you run into some First Amendment issues. There are literally hundreds of gunsmithing guides on Amazon, are we going to ban those books, too? Under the Undetectable Firearms Act of 1998, the mere possession of any gun that would avoid a metal detector is already a crime."