Washington (CNN) President Donald Trump Tuesday signed a measure nixing a regulation aimed at keeping guns out of the hands of some severely mentally ill people. 
 
 The original rule was part of a series of efforts taken by the Obama administration to try and curb gun violence after other efforts failed to advance in Congress. 
 
 Using the Congressional Review Act -- which allows Congress to roll back regulations imposed by the executive branch -- the Republican-controlled House and Senate voted to send the bill to Trump's desk. 
 
 What was the rule? 
 
 The regulation, finalized in December under Obama's tenure, required the Social Security Administration to disclose information quarterly to the national gun background check system about certain people with mental illness. 
 
 While the list of eligible mental disorders is long -- ranging from anxiety to eating disorders to schizophrenia --those who would have been reported by the agency had to meet two main criteria: a) They were receiving full disability benefits because of a mental illness and couldn't work and b) they were unable to manage their own benefits, thus needing the help of a third party to do so. 
 
 The Obama administration estimated that the new rule would have affected roughly 75,000 individuals annually. 
 
 And according to a report by the Office of the Inspector General at the Social Security Administration, 81,000 disability awardees would have met the criteria in fiscal year 2015, which amounts to about 9% of the total disability awardee population. 
 
 Those affected would have been notified both orally and in writing that they could potentially be prevented from buying a gun. 
 
 Such individuals would have been allowed to request a relief from any firearm prohibitions if they could show evidence that they didn't pose a risk to public safety. 
 
 While the rule wasn't effective until January 18, compliance was not required until later this year -- in December. So it's unlikely that anyone has been affected by the rule. 
 
 Who opposed the rule? 
 
 Interestingly, the rule had opponents across a wide spectrum. Both the National Rifle Association and the American Civil Liberties Union spoke out against it. 
 
 The ACLU, which advocates for people with mental health struggles, said the rule reinforced a stereotype that people with mental disabilities are violent. The organization argued in a letter to members of Congress that there's no data to support a connection between receiving disability benefits and a propensity toward gun violence. 
 
 Susan Mizner, senior attorney with the disability rights program at the ACLU, also said that people with mental illnesses are more likely to be victims of violence. 
 
 While proponents of the rule argue that it only affects a limited group, opponents say that it unfairly targets the wrong people. 
 
 "75,000 people a year is a lot of people in my book," Mizner said. "And these are people who are already at the bottom of our social status. We don't need to kick them anymore." 
 
 Who supported it? 
 
 Gun control groups and activists supported the rule because they felt it would prevent some suicides and accidental deaths. 
 
 They argued that it helped enforced laws already in the books that require mental health reporting by federal agencies, said Lindsay Nichols, senior attorney with the Law Center to Prevent Gun Violence. 
 
 "The American people and the families that are being hurt day after day by gun violence -- they deserve some due process too," said Rep. Lloyd Doggett, D-Texas. ||||| Breaking News Emails Get breaking news alerts and special reports. The news and stories that matter, delivered weekday mornings. 
 
 / Updated By Ali Vitali 
 
 President Donald Trump quietly signed a bill into law Tuesday rolling back an Obama-era regulation that made it harder for people with mental illnesses to purchase a gun. 
 
 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. 
 
 Related: Assault Weapons Not Protected by Second Amendment, Federal Appeals Court Rules 
 
 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. 
 
 Both the House and Senate last week passed the new bill, H.J. Res 40, revoking the Obama-era regulation. 
 
 Trump signed the bill into law without a photo op or fanfare. The president welcomed cameras into the oval office Tuesday for the signing of other executive orders and bills. News that the president signed the bill was tucked at the bottom of a White House email alerting press to other legislation signed by the president. 
 
 The National Rifle Association “applauded” Trump’s action. Chris Cox, NRA-ILA executive director, said the move “marks a new era for law-abiding gun owners, as we now have a president who respects and supports our arms.” 
 
 Everytown For Gun Safety President John Feinblatt said he expected more gun control rollbacks from the Trump administration. In a statement to NBC News, he called the action "just the first item on the gun lobby’s wish list" and accused the National Rifle Association of "pushing more guns, for more people, in more places." 
 
 Sen. Chris Murphy, D-Conn., a leading gun control advocate in Congress, called out Republicans over the move. 
 
 "Republicans always say we don’t need new gun laws, we just need to enforce the laws already on the books. But the bill signed into law today undermines enforcement of existing laws that Congress passed to make sure the background check system had complete information," he said in an emailed statement.
– President Trump has undone one of his predecessor's final executive actions, a measure designed to make it harder for the mentally ill to own guns. The issue is a little more complicated than the usual gun-control debate, however: This time, both the NRA and the ACLU opposed the measure. The move by President Obama in December required the Social Security Administration to provide information about people who met certain criteria to the national database for background checks, reports NBC News. Affected would be those who get full disability benefits because of a mental illness and who were deemed unfit to manage their own finances, explains CNN. They were to be notified that they might not be eligible to own a gun, though they could appeal. The Obama administration estimated it would apply to 75,000 people. Last week, the House and Senate passed a bill to undo the rule, and Trump signed it into law on Tuesday. He had promised to "un-sign that [bill] so fast" even before he became president, reports USA Today. It was criticized by both the ACLU, which said it added to the stereotype that equates mental illness with violence, and the NRA, which opposed it on Second Amendment grounds. The head of the NRA's Institute for Legislative Action says the move "marks a new era for law-abiding gun owners, as we now have a president who respects and supports our arms." Gun-control advocates say the law would've prevented suicides and accidental deaths.