The Republican-backed language, introduced by Sen. John Thune, R-S.D., would override stricter laws of many jurisdictions, giving preference to states with looser standards, The Washington Post reported Tuesday.
Thune offered the amendment Monday to the defense authorization bill. The language would allow people to carry concealed firearms across state lines as long as they "have a valid permit or if, under their state of residence ... are entitled to do so."
On two gun-rights measures this session, Republicans peeled off votes moderate Democrats elected from states with strong Second Amendment traditions. In May, 27 Democrats supported eased restrictions on firearms in state parks and in February, 22 Democrats joined Republicans to freeze the District of Columbia's pursuit for House voting rights by demanding the legislation also relax D.C. gun restrictions.
In a statement, Thune characterized his amendment was a crime-prevention tool, the Post said.
"Since criminals are unable to tell who is and who is not carrying a firearm just by looking at a potential victim, they are less likely to commit crimes when they fear that they may come in direct contact with an individual who is armed," he said.
Sen. Charles Schumer, D-N.Y., who pledged to filibuster the amendment, said it scuttled states' rights.
"Each state has carefully crafted its concealed-carry laws in the way that makes the most sense to protect its citizens," he said. "To gut the ability of local police and sheriffs to determine who should be able to carry a concealed weapon makes no sense."