Maricopa County Sheriff Paul Penzone has been an outspoken critic of allowing the distribution of blueprints to create plastic guns with 3D printers.
If that happened, Penzone says it would be an irresponsible action that can't be reversed.
On Tuesday, a federal judge in Seattle stopped the scheduled release of blueprints to make untraceable and undetectable 3D-printed guns.
An Austin, Texas company had reached a settlement with the federal government in June allowing it to make the plans for the guns available for download.
The restraining order puts that plan on hold for now.
Penzone told Phoenix radio station KTAR he's concerned about drug cartels or terrorists groups who could afford to invest in the expensive printers.
He says those people could create untraceable weapons that would thwart metal detectors.