California State Senator Leland Yee (who represents the western part of San Francisco) announced that he will pursue outlawing 3-D-printed weaponry, in the wake of the first 3-D-printed gun to be successfully fired.
This weekend, a Texas group called Defense Distributed created the plans for a 3-D-printed gun made almost entirely of plastic--the only metal part is a very small firing pin. (For more on that, check out this article.) Federal law restricts the purchase of guns--barely--but places no restrictions on the creation of weaponry.
That hasn't been much of a problem in the past; while it's certainly possible to use various metalworking machines to create a working firearm, it's expensive and difficult, requiring quite a bit of expertise, and when it's easy and cheap to buy a professionally made gun (legally or illegally), homemade guns haven't caught on.