The alternative: face possible prosecution for violating regulations that forbid the international export of unapproved arms.

Now Wilson is challenging that letter. And in doing so, he's picking a fight that could pit proponents of gun control and defenders of free speech against each other in an age when the line between a lethal weapon and a collection of bits is blurrier than ever before.

Wilson's gun manufacturing advocacy group Defense Distributed, along with the gun rights group the Second Amendment Foundation, on Wednesday filed a lawsuit against the State Department and several of its officials, including Secretary of State John Kerry. In their complaint, they claim that a State Department agency called the Directorate of Defense Trade Controls (DDTC) violated their first amendment right to free speech by telling Defense Distributed that it couldn't publish a 3-D printable file for its one-shot plastic pistol known as the Liberator, along with a collection of other printable gun parts, on its website.