The Republican-led House of Representatives has voted to overturn an Obama-era regulation preventing people with severe mental illnesses from buying guns.
The vote on Thursday (local time) was 235-180 - mostly along party lines.
Under the Obama administration's rule, people who receive disability benefits and have severe mental disorders would be reported by the Social Security Administration to the FBI's National Instant Criminal Background Check System.
This database is used to determine eligibility for buying a firearm.
However it was strongly opposed by both the Republican Party and the National Rifle Association.
"The Social Security Administration not only overstepped its mission with this regulation, it discriminated against certain Americans with disabilities who receive Social Security benefits," said Republican Representative Kevin Brady.
"The agency should be focused on serving all of its beneficiaries, not picking and choosing whose Second Amendment rights to deny."
Other Republicans argued the rule unfairly stigmatised people with mental disabilities.
"This is a slap in the face for those in the disabled community because it paints all those who suffer from mental disorders with the same broad brush," said Republican Representative Bob Goodlatte.
"It assumes that simply because an individual suffers from a mental condition, that individual is unfit to exercise his or her Second Amendment rights."
However, Democrats say the rule is needed to keep guns away from people with severe mental disorders like schizophrenia.
"The American people and the families that are being hurt day after day by gun violence - they deserve some due process too," said Democrat Representative Lloyd Doggett.
The Senate is expected to pass the measure soon and President Donald Trump is expected to sign it. Democrats warn this will lead to more gun violence and shooting sprees.
"These are not just people having a bad day," said Democrat Representative Mike Thompson.
"These are not people simply suffering from depression or anxiety. These are people with a severe mental illness who can't hold any kind of job or make any decisions about their affairs. So the law says very clearly they shouldn't have a firearm."