U.S. Senators reached an agreement that would expand background checks for firearm purchases to limit access to weapons for criminals and the mentally ill.

Senators Joe Manchin (D-W.Va.) and Patrick Toomey (R-Pa.) spearheaded the deal, reports the New York Times. The deal that will receive a Senate vote on Thursday would expand background checks to gun shows and online purchases. The announcement came as victims of the Sandy Hook Elementary shooting headed to Washington, D.C. to voice support for gun-violence measures.

The National Rifle Association released a statement denouncing the proposed amendment.

"The sad truth is that no background check would have prevented the tragedies in Newtown, Aurora or Tucson," according to the statement. "We need a serious and meaningful solution that addresses crime in cities like Chicago, addresses mental health deficiencies, while at the same time protecting the rights of those of us who are not a danger to anyone."

The New York Police Department has said that 90% of the guns recovered in crimes in the city originate out of state from Pennsylvania, Virginia, North Carolina, South Carolina, and Florida. On Wednesday, Commissioner Paul Browne told POLICE Magazine the department supports the measure, but added that it wouldn't address criminal straw purchasers who buy guns in those states.

"The straw purchaser from New York has a criminal record," Browne said. "He's producing the cash for the guns. The only thing he's not doing is filling out the paperwork."

However, Browne said the proposed legislation could prevent gang members or the mentally ill from purchasing pistols or rifles at gun shows if the background checks flag illegal buyers.

"Does that mean it's going to stop everyone from acquiring a gun illegally? Probably not. It would be a check and an opportunity to stop that person from acquiring a gun," Browne added.

Others say expanded background checks will only further push illegal buyers underground.

"Universal background checks won't drastically reduce crime in New York or elsewhere," said Adam Winkler, author and UCLA law professor. "For the hardened criminal, background checks will just push them further into the black market.

By Paul Clinton