Sen. Richard Burr, R-N.C. speaks on Capitol Hill in Washington in 2015. (AP Photo/Jacquelyn Martin, File)

A Republican super PAC with ties to Senate Majority Leader Mitch McConnell is reserving $8.1 million in ad buys to aid North Carolina Sen. Richard Burr, who is facing an increasingly competitive re-election bid against Democratic challenger Deborah Ross.

The TV ad buy, first reported by Roll Call, will begin Sept. 13. The investment by Senate Leadership Fund signals Republicans are wary that Burr, once considered a safe bet to win re-election and help preserve the GOP majority in the Senate, may lose to the little-known Ross, a former ACLU state director and state legislator.

A poll released Tuesday by Emerson College shows Burr leads Ross, 45 to 41, with a 3.4 percent margin of error. Two other polls released last week by Monmouth University and CNN/ORC showed Burr leading by two points and three points, respectively.

The move by Senate Leadership Fund, which is led by McConnell’s former chief of staff Steven Law, marks a significant ramp-up in spending in the state by outside groups, which spent about $667,000 on the North Carolina Senate race through Aug. 30, according to Federal Election Commission data. The two largest infusions of cash came from the NRA’s super PAC, which spent $272,000, and Clearpath Action, the GOP clean energy group backed by North Carolina businessman Jay Faison, which spent $202,000. Both groups’ ads support Burr. Women Speak Out PAC has spent $46,000 on canvassing efforts urging voters to oppose Ross.

The Burr campaign welcomed the new ad buy from Senate Leadership Fund.

“Voters deserve to know how dangerous former ACLU lobbyist Deborah Ross would be for North Carolina and we welcome anyone who wants help point it out,” said Jesse Hunt, a spokesman for the Burr campaign.

One Nation, the nonprofit arm of Senate Leadership Fund, announced a $1 million TV ad buy last week in support of Burr.

“It’s no surprise that, like a typical Washington politician, [Burr]’s turning to the same big money donors he’s put first all along,” Ross’s campaign spokesman Cole Leiter said in a statement Thursday. “But North Carolina voters won’t be fooled — they know it’s time for a change, and no amount of special interest dark money can bail Richard Burr out.”


Anu Narayanswamy contributed to this report.

Correction: A previous version of this story incorrectly stated how Women Speak Out PAC spent its money.