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There's a new big spender in Georgia.

EMILY's List, the political action committee that supports pro-abortion-rights Democratic female candidates, has bought $1 million of air time in Atlanta's media market to run a TV ad attacking the business record of Republican Senate candidate and former Dollar General CEO David Perdue, the group told ABC.

The $1 million ad buy will be the largest single outside expenditure in the race to date, topping a $920,000 U.S. Chamber of Commerce ad buy in April.

Michelle Nunn, the Democrats' nominee to replace retiring Sen. Saxby Chambliss, R-Ga., is one of the party's brighter stars in this election cycle, but she faces an uphill climb to defeat Perdue in a state that hasn't voted statewide for a Democrat since 2000. The last major survey of the race, a CBS/New York Times/YouGov poll conducted from July 5 to 25, showed Perdue leading Nunn by 6 percentage points.

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The ad, which has not yet been made public, will focus on a gender pay discrimination suit brought by female store managers claiming Dollar General had underpaid them during Perdue's tenure. Dollar General settled the suit in 2011 after Perdue had left as CEO, a role he held from 2003 to 2007.

A court allowed a class-action suit in 2007 for women who had worked as Dollar General store managers from 2004 to 2007, and 2,100 opted into it, according to an SEC report. Dollar General agreed to pay $19 million as part of a settlement in 2011, Law360 reported.

More than 140 Georgia women joined the suit, EMILY's List points out.

"David Perdue owes Georgians answers about his shady business dealings that put his own profits ahead working women," EMILY's List spokeswoman Marcy Stech said. "And he certainly needs to be straightforward with the women of Georgia who deserve to know if he still believes it's OK to pay women less than men for the same job."

Perdue has faced attacks on his business record before. In his primary runoff, Kingston aired ads that highlighted lost jobs at a company Perdue led and a government bailout for another on whose board Perdue sat. Nunn's campaign went up with a negative ad this week featuring workers who lost their jobs at textile firm Pillowtex under the leadership of Perdue, who ran the company after it emerged from bankruptcy.

With the new ad from EMILY's List, Nunn will have her most significant outside help so far and, compared to her GOP rival, she may need it.

While today's individual buy is the biggest to date, EMILY's List is by no means the race's aggregate money leader when it comes to outside groups.

Republican groups have swarmed Georgia, spending millions there already, much of it on the competitive (and overwhelmingly negative) seven-way GOP primary and Perdue's runoff against Rep. Jack Kingston, R-Ga. The Chamber, for instance, spent $2.9 million backing Kingston.

A GOP super PAC called the Ending Spending Action Fund has spent $3.1 million, some of it on the GOP primary, and some of it attacking Nunn. The American Chemistry Council has spent $1.4 million backing Perdue, and a pro-Perdue super PAC called Citizens for a Working America has spent over $2 million.