Pelosi accused Republicans of doing the bidding of the National Rifle Association, which calls the concealed-carry law its top legislative priority.
'Two months after two of the most deadly shootings in modern American history, Republicans are brazenly moving to hand the NRA the biggest item on its Christmas wish list,'' Pelosi, D-Calif., said in a statement.
'Far from making Americans safer, this deadly, extreme Republican bill would make it legal for more dangerous and untrained people to carry loaded, hidden guns in more public places and would inexplicably try to make the weakest and most dangerous state concealed-carry laws the law of the land in all 50 states,'' she said.
Republicans said the bill would allow gun owners to travel freely without worrying about conflicting state laws or civil suits.
Lawmakers expect House action on Wednesday.
The bill includes a provision to strengthen the FBI database of prohibited gun buyers after the Air Force failed to report the criminal history of the gunman who slaughtered more than two dozen people at a Texas church.
Gun shop owner Tiffany Teasdale-Causer returns a Ruger AR-15 semi-automatic rifle, the same model, though in gray rather than black, used by the shooter in a Texas church massacre two days earlier, to it';s place on a wall with dozens of other semi-automatic rifles, Nov. 7, 2017, in Lynnwood, Washington.
The Air Force has acknowledged that the Texas shooter, Devin P. Kelley, should have had his name and domestic violence conviction submitted to the National Criminal Information Center database. The Air Force has discovered several dozen other such reporting omissions since the Nov. 5 shooting.
If the concealed-carry bill is approved by the House and Senate and signed into law, key state and local laws protecting against gun violence could be overridden, Pelosi said, 'inviting concealed weapons into schools, churches, bars and public lands.''
The bill is the latest 'but certainly not the last Republican attempt to wipe out common-sense'' gun laws, she said, citing GOP efforts to block legislation tightening laws on background checks, refusal to create a bipartisan Select Committee on Gun Violence and a push to ease restrictions on silencers and armor-piercing bullets.