The rule, which was finalized in December, added people receiving Social Security checks for mental illnesses and people deemed unfit to handle their own financial affairs to the national background check database.
Had the rule fully taken effect, the Obama administration predicted it would have added about 75,000 names to that database.
President Barack Obama recommended the now-nullified regulation in a 2013 memo following the mass shooting at Sandy Hook Elementary School, which left 20 first graders and six others dead. The measure sought to block some people with severe mental health problems from buying guns.
The original rule was hotly contested by gun rights advocates who said it infringed on Americans' Second Amendment rights. Gun control advocates, however, praised the rule for curbing the availability of firearms to those who may not use them with the right intentions.
