A newly formed super PAC, which has yet to make public the sources of its funding, has just dropped $1 million in negative ads against Michigan Sen. Debbie Stabenow.

The Hardworking Americans Committee, which registered with the Federal Election Commission in late September, will be "disclosing our donors when the FEC requires us to disclose,"Stuart Sandler, a former official with the Michigan Republican Party who is serving as the group's treasurer, told Sunlight. Asked to characterize the super PAC's contributors, Sandler said that they are "a group of hardworking Americans who like Pete Hoekstra," the Republican running against Stabenow. Hoekstra is a former Republican congressman who left his House seat two years ago to run unsuccessfully for Michigan governor.

Hardworking Americans is one of the newest members of the October Surprise Club, political committees that have only become visible on the political radar in the last month before Election Day. Sunlight is compling a list of them here.  The first time spenders have spent at least $13 million on House and Senate races as well as the presidential contest.

The 39 late-spending groups that have surfaced so far are about evenly divided by partisan tilt: 20 are clearly Democratic, 16 are Republican and four are making electioneering expenditures which are harder to categorize. Some are well-known entitities with long track records of political giving; others are newcomers with vague-sounding names that make their agendas harder to track.

Among the million dollar late-spenders is NFIB The Voice of Free Enterprise, which has circulated $1.8 million supporting Republicans in various House and Senate races, mostly on mailings and online ads. The group is an offshoot of the National Federation of Independent Business, a roundtable for small businesses, which has already spent another $1.4 million as independent expenditures via it’s political action committee. In the first presidential debate, Republican candidate Mitt Romney cited NFIB estimates to argue that President Barack Obama's plan to raise taxes on upper-income earners would cost 700,000 jobs. In 2010, the group was part of the lawsuit against the healthcare law and received a few million from the Crossroads GPS, headed by Karl Rove, according to media reports.

Another new group, the Citizen Awareness Project, has spent more than $1 million opposing Obama in the battleground state of Colorado.

The Massachusetts Senate race, which surprisingly saw little outside spending earlier, is picking up steam with groups spending a total of $3.6 million, including a recent $442,000 mailer buy opposing the Democrat Elizabeth Warren, from the group America 360 committee. Although the group was founded in January, recently they've been flushed with cash after William Koch’s Oxbow Carbon, LLC., among other donors, wrote a hefty check worth $500,000.

A number of the October surprise club members are, like Hardworking Americans, focusing on one or two contests, meaning that their last-minute contributions can have a major impact. Sunlight earlier wrote about another such group, the Government Integrity Fund Action Network, which just dropped $1.1 million into a competitive Connecticut House race.

Hardworking Americans' single contribution represents a major boost for Hoekstra, who as of Sept. 30 had raised $4.8 million to Stabenow's $13.6 million. It also represents almost half of the outside expenditures made in the Michigan Senate race so far.

Michigan is a traditional political battleground, and Stabenow had seemed vulnerable earlier in the campaign but nonpartisan political prognosticator Charlie Cook has more recently given her a better-than even chance to hold onto her seat. The RealClearPolitics average of polls also gives her a comfortable lead.

Though Sandler described Hardworking Americans as a group of Hoekstra supporters, the ad they are running, seen above, is focused solely on Stabenow, citing her failure to pay property taxes on a Washington home five years ago. A spokesman for the senator acknowledged late tax payments to the Detroit News but the newspaper found that Stabenow has keep payments current for the last five years.

Sandler, who runs a Michigan-based political consulting firm, is a longtime GOP activist who recently served as executive director of the Michigan Republican Party. 

(Contributing to this story: Anupama Narayanswamy, Jacob Fenton, Lindsay Young and Kathy Kiely)