Editor's note: This story has been updated with UPS's statement on its refusal to ship digital milling machines used to create firearms.

The new generation of "maker" tools like 3-D printers and milling machines promises to let anyone make virtually anything—from prosthetic limbs to firearms—in the privacy and convenience of his or her own home. But first, those tools have to get to customers' homes. That's going to be difficult for at least one new machine with the potential to make homemade firearms, because FedEx is refusing to deliver it.

Last week FedEx told firearm-access nonprofit Defense Distributed that the company refuses to ship the group's new tool, a computer controlled (CNC) mill known as the Ghost Gunner. Defense Distributed has marketed its one-foot-cubed $1,500 machine, which allows anyone to automatically carve aluminum objects from digital designs, as an affordable, private way to make an AR-15 rifle body without a serial number. Add in off-the-shelf parts that can be ordered online, and the Ghost Gunner would allow anyone to create one of the DIY, untraceable, semi-automatic firearms sometimes known as "ghost guns."

When the machine was revealed last October, Defense Distributed's pre-orders sold out in 36 hours. But now FedEx tells WIRED it's too wary of the legal issues around homemade gunsmithing to ship the machine to customers. "This device is capable of manufacturing firearms, and potentially by private individuals," FedEx spokesperson Scott Fiedler wrote in a statement. "We are uncertain at this time whether this device is a regulated commodity by local, state or federal governments. As such, to ensure we comply with the applicable law and regulations, FedEx declined to ship this device until we know more about how it will be regulated."

But buying, selling, or using the Ghost Gunner isn't illegal, nor is owning an AR-15 without a serial number, says Adam Winkler, a law professor at UCLA and the author of Gunfight: The Battle over the Right to Bear Arms in America. "This is not that problematic," he says. "Federal law does not prohibit individuals from making their own firearms at home, and that includes AR-15s."

Defense Distributed's founder Cody Wilson argues that rather than a legal ambiguity, FedEx is instead facing up to the political gray area of enabling the sale of new, easily accessible tools that can make anything—including deadly weapons. "They're acting like this is legal when in fact it's the expression of a political preference," says Wilson. "The artifact that they’re shipping is a CNC mill. There's nothing about it that is specifically related to firearms except the hocus pocus of the marketing."

Wilson, whose radically libertarian group has pursued projects ranging from 3-D printed guns to untraceable cryptocurrency, says he chose to ship his Ghost Gunner machines with FedEx specifically because the company has a special NRA firearm industry membership. But when he told a local FedEx representative what he'd be shipping, he says the sales rep responded that he'd need to check with a superior. "This is no big deal, right? It’s just a mill," Wilson says he told his FedEx contact. "You guys ship guns. You’ve shipped 3-D printers and mills, right? You’ll ship a drill press, right? Same difference."

Last week the FedEx rep told Wilson in a phone conversation that it wouldn't ship his mills, though it didn't offer any legal or policy explanation of the decision until WIRED's inquiry. After its statement about the Ghost Gunner's questionable legality, FedEx spokesperson Fiedler declined to comment further on its decision not to ship the devices. Fiedler pointed me to a list of items FedEx won't ship, ranging from hazardous waste to human corpses. He noted that it also includes marijuana, an example of an item that's banned by FedEx despite being legal in some states. The list doesn't include anything about guns or gun-making tools.

The US Postal Service didn't immediately respond to questions about whether they would allow the shipment of the Ghost Gunner or other potential gunsmithing devices. A UPS spokesperson wrote in a statement that the company will only ship guns and gun parts between holders of a federal firearms license. In a follow-up statement, it confirmed that it won't ship the Ghost Gunner either. "UPS reserves the right to refuse to provide transportation service for, among other reasons, any shipments that create legal, safety or operational concerns," writes spokesperson Dan Mackin. "UPS is continuing to evaluate such concerns with regard to the transportation of milling machines used to produce operable firearms but, at this point in time, will not accept such devices for transportation."^1 2^

FedEx's and UPS's decisions seem to be another test case for the new, politically fraught era of powerful, general purpose consumer manufacturing machines. Just as personal computers can be used for everything from biological research to malicious hacking, 3-D printers and CNC mills will also enable plenty of dangerous objects to be made along with garden gnomes and gadget prototypes.

The Ghost Gunner is technically a multipurpose milling machine that could make a variety of metal objects. But it's not marketed for making garden gnomes; Everything from the machine's name to a marketing video showing it being used to make an serial-numberless AR-15 makes clear that the device's primary purpose is manufacturing guns. “This is a way to jab at the bleeding hearts of these total statists,” Wilson told WIRED in October. “It’s about humiliating the power that wants to humiliate you.”

Gun enthusiasts have been legally milling their own AR-15 lower receivers—the regulated body of the gun—for years using more expensive tools, and more recently 3-D printing them in plastic. A California bill to outlaw the home manufacture of unserialized firearms was vetoed by the state's governor, Jerry Brown, who wrote in his veto letter that he "can’t see how adding a serial number to a homemade gun would significantly advance public safety.”

Of course, the controversy around Defense Distributed is far more than legal; plenty of other companies have opted to keep their distance. Indiegogo booted the group's initial fundraiser off the site in 2012. And 3-D printer maker Stratasys refused to continue renting a printer to the group after learning that its machine was being used to make gun components.

FedEx seems to be joining the same club of companies trying to avoid any part in digital DIY gunsmithing. But as more tools like 3-D printers and CNC mills find their way into Americans' homes, they may have to face the reality that those devices can also create deadly weapons, says UCLA's Winkler. "It’s going to be very hard to get people to stop using these same devices to make firearms," he says. "To a certain extent, FedEx will have to get used to shipping gun-making machines."

1Updated 2/24/2015 3:15pm EST with a statement from UPS.

2Updated 2/25/2015 11:25am EST with a second statement from UPS.