The PAC’s ad criticizes Buchanan for receiving $15,450 from the NRA, the Sun-Sentinel reported.
Federal Election Commission records showed the PAC spent $12,000 as part of the ad campaign this week.
Giffords resigned from Congress in 2012 after being shot in the head during a constituent event in Arizona.
She and her husband, retired astronaut and Navy Capt. Mark Kelly, have since become an advocate for tighter gun laws and founded her PAC in 2013 after the shooting at Sandy Hook Elementary School. Buchanan is the only Florida member Giffords’ group has targeted so far.
Watch: Which House Races Are the Parties Targeting? Look to the Money
In the weeks after the shooting at Marjory Stoneman Douglas High School in Parkland, Giffords’ group said it spent a “strong six figures” targeting Republican Gov. Rick Scott ahead of his announcement he would challenge Democratic Sen. Bill Nelson.
The group’s political director Isabelle James said it plans to spend $5 million in elections this cycle.
“We are looking at races where we really believe this issue is going to make a difference, where it’ll rise to the top of the list for voters,” James said.
Giffords’ group also endorsed Buchanan’s Democratic opponent, personal injury lawyer David Shapiro.
Along with Buchanan’s race, James said it’s “quite likely” the group will spend money on Florida’s Senate race and against Republican Rep. Mario Diaz-Balart.