Updated 10:15 p.m. ET, Wednesday, 6/12
(CNN) - The National Rifle Association is running a political ad against one of its own.
Sen. Joe Manchin, an avowed gun enthusiast and life member of the NRA, is now being hit with an ad from the organization in his home state of West Virginia.
Manchin was one of the leading voices in the Senate for a bipartisan effort to expand the background check system on firearm sales. A conservative Democrat, Manchin made news in December when he said the Newtown elementary school massacre changed his views on gun control.
According to NRA spokesman Andrew Arulanandam, it is paying $100,000 to run the ad in heavy rotation during newscasts in West Virginia.
The group is also running a radio ad supporting Sen. Mark Pryor, a Democrat from Arkansas who went against his own party and voted against the background check measure in April. Pryor has been the target of pro-gun control groups since the vote.
The 30-second commercial against Manchin features footage from an ad for his 2010 Senate campaign in which he boasts of his NRA endorsement and shoots a copy of the Cap and Trade bill.
"But now, Manchin is working with President Obama and New York Mayor Michael Bloomberg," the narrator says in the new NRA ad. "Concerned? You should be. Tell Sen. Manchin to honor his commitment to the Second Amendment and reject the Obama-Bloomberg gun control agenda."
Manchin does not face re-election until 2018, giving him more political leeway than others in the Senate to make big moves on controversial issues. He was also endorsed by the NRA political victory fund in his 2012 Senate campaign.
The new NRA ad comes as the gun control debate has seen renewed attention this week, which marks six months since the Sandy Hook shooting. Several Newtown, Connecticut, families met with Manchin on Wednesday in Washington.
"I've been all over the state of West Virginia. There's not a state I believe that cherishes its Second Amendment rights and has a gun culture more than our state, and yet I talk to my gun friends and all the people I shoot and hunt with, and they believe it makes sense," he said of the background check measure, while meeting with the families in his office.
- By CNN's Steve Brusk and Ashley Killough.