It's an indication, the group says, that it's willing to go as far as it takes to combat attacks from pro-gun control groups on Ayotte's vote last month opposing a proposal to expand background checks.

Following polling that showed the vote hurt Ayotte's support in her home state, a group backed by former Rep. Gabby Giffords (D-Ariz.) launched radio ads hitting the senator, and Mayors Against Illegal Guns, which is supported by New York City Mayor Michael Bloomberg, issued television ads hammering her.

A recent poll showed New Hampshire voters split on Ayotte but seeing her slightly more favorably, with 48 percent approving of her job performance and 43 percent disapproving of her work.

She's not up for reelection until 2016, but gun control advocates see her as one of the likeliest senators to switch their vote if they succeed in bringing the bill back up in Congress.

But a number of conservative groups have come out with ads of their own to counter the attacks, including one from the National Rifle Association and another from Sen. Marco RubioMarco Antonio RubioLobbying world Former Florida congressmen mull bipartisan gubernatorial run: report Winners and losers from Jim Bridenstine’s confirmation as NASA administrator MORE's (R-Fla.) PAC, touting her support for measures to curb gun violence.

AFF's ad features New Hampshire voters and law enforcement officers outlining what they characterize as Ayotte's work to curb gun violence in the state.

The buy now totals $550,000, and the ad will run on Manchester cable and network television, as well as in Boston, through May 27.

Matt Beynon, spokesman for AFF, said that the group had seen an "encouraging" response since it first went up on air.

"The response to the initial ad buy has been very encouraging, so we decided to expand the ad buy beyond just Manchester and into the Boston market as well. We do not want Mayor Bloomberg’s misleading attacks to go unanswered, and this is part of that continued campaign," he said.