The U.S. Chamber of Commerce is not the only business group that has been boosting its Congressional allies this political season.

The National Federation of Independent Business, which has been critical of key elements of President Barack Obama’s agenda, including health care reform, is underwriting a media campaign that could total as much as $6 million, according to group spokeswoman Stephanie Cathcart.

The most recent salvo from the NFIB came this week with the release of television spots against nine House Democrats.

The ad buy, worth about $3 million, asks voters to call their Member of Congress to express concern about wasteful government spending.

The trade group, which represents small businesses, is also undertaking grass-roots activities that Cathcart said were based on “almost a union-organizing model.”

She said the NFIB was sending out letters advising its members how they can volunteer to help candidates whom the group supports. It is also providing a website that includes a link for employers to print posters and paycheck stuffers to give their employees information on how they can volunteer with or make financial donations to campaigns. And the NFIB has printed a first-ever hard copy of its Small Business Voter Guide, which includes a list of candidates endorsed by the group.

Beginning Oct. 25, Cathcart said, the “NFIB road team,” comprised of the trade group’s staffers, will fan out across the country to talk to local businesses about the key issues facing them.

But while the unions flex their political muscle largely on behalf of Democrats, the NFIB has thrown its support mostly to Republicans.

In its endorsements of more than 200 gubernatorial and federal candidates this cycle, only a handful went to Democrats, including Reps. Bobby Bright (Ala.), Jim Marshall (Ga.), Walt Minnick (Idaho), Dan Boren (Okla.) and Glenn Nye (Va.).

In addition, the NFIB’s political action committee has given more than 90 percent of its contributions to federal candidates to Republicans so far this election cycle. That compares to just more than 82 percent in the 2008 cycle and 89 percent in 2006.

Among the Republicans whom the NFIB is backing this year is Sen. Lisa Murkowski (Alaska), who lost her primary race to tea-party-supported candidate Joe Miller. Murkowski, who is waging a general election campaign as a write-in candidate, has actively solicited financial support from K Street lobbyists, many of whom have backed her in the past.

Cathcart said Murkowski had a 100 percent approval rating in key votes tallied by the NFIB.

“We endorsed her prior to the primary for her longtime support of small business and don’t make a distinction between primary and general election endorsements,” she said. “However, we aren’t actively engaging in the write-in race going on there.”

The latest television spots, which are running through Oct. 23, are playing in House districts in California, Colorado, Missouri, New York, Ohio, Pennsylvania, South Carolina and Wisconsin. The NFIB has classified this advertising as issue-oriented and thus it will be reported as part of the organization’s lobbying expenses rather than as election activity. Earlier this fall, the NFIB ran $600,000 in radio spots, which were reported as independent expenditures related to the elections.

As part of his economic policies, Obama has stressed his support for small businesses, recently signing legislation aimed at helping that sector. But the NFIB has not signed on to much of his agenda and has been particularly vocal in its opposition to the new health care law, which the group argues will increase costs and regulations for small businesses.

The NFIB has joined a lawsuit challenging the constitutionality of the health care law, including its mandate that adults buy health insurance policies.

Cathcart said the group was “indifferent” to the small-business measure signed by Obama. She said that while it offered some provisions that could help some small businesses, they would have to take proactive measures to take advantage of the benefits.

While the NFIB plans to dole out millions of dollars on the campaigns, its spending still pales in comparison to the U.S. Chamber of Commerce, which has reported shelling out more than $21 million on television ads and other election activities this year, including almost $12 million during the week of Oct. 4.

The chamber’s spending has come under attack from Obama, liberal groups and Democrats, who have suggested that some of the money may have come from foreign sources.

But in a letter to the chamber’s board of directors earlier this week, chamber President Tom Donohue said the funds that his group receives from foreign entities “are never used to support any political activities.”

Donohue ripped the White House and its allies for their attacks on the chamber and vowed that his group would not be silenced.

“In fact, for the next three weeks leading up to Election Day, you will see us ramp up efforts to educate voters about the positions of candidates of both parties who are committed to free enterprise and economic growth,” he said in the Tuesday letter.

However, as of close of business Friday, the chamber had not reported any additional election-related spending for the current week to the Federal Election Commission.

Alex Knott contributed to this story.