Sen. Sherrod Brown speculates that funds for the ads come form the oil industry, the Chinese, and Wall Street.
A new political commercial that has been running frequently on Toledo television stations shows a grainy image of Sen. Sherrod Brown peeping through window blinds. An equally grainy image shows a man running crazily away from the camera.
The voice-over: "Sherrod Brown can run but he can't hide from his record."
At the end is the notation "Paid for by the U.S. Chamber of Commerce."
The ad is one of a series of recent TV commercials and Web ads paid for by national groups seeking to influence Ohio voters in the 2012 election for the U.S. Senate.
The seat was won in 2006 by Mr. Brown, who is a Democrat from Avon.
The leading Republican candidate is Ohio Treasurer Josh Mandel.
"With the state of the economy in Ohio, it is important to have a debate on where the candidates stand on these issues," said J.P. Fielder, a spokesman for the U.S. Chamber of Commerce. "So let's talk about the specifics of where Sherrod Brown stands on the energy issue."
Democrats supporting Mr. Brown for re-election have attacked the ads as misleading or outright false.
Senator Brown dismissed the ads while on a news conference call Wednesday with Ohio reporters.
"I think these ads are cynical. PolitiFact has found much of the info in these ads to just be -- they call it 'pants on fire' -- outright lies," Mr. Brown said, citing the Web-based news organization that examines political ads.
He said the sources of political contributions to the Chamber of Commerce aren't known, so he speculated that they are the oil companies because of his support for closing oil-company tax breaks, the Chinese because of his efforts to fight outsourcing, and Wall Street.
"Know me by my enemies," he said. "The problem is they don't have to disclose where the money comes from."
The latest TV ad claims that Mr. Brown wants to "raise energy taxes" and that he voted to raise taxes on small businesses by voting for the national health-care law. Those policies, according to the commercial, "kill American jobs" and are "making Ohio's economy worse."
On energy taxes, the ad makes reference to Senator Brown's support of a bill to abolish tax breaks for the oil industry.
FactCheck.org, an operation of nonprofit Annenberg Public Policy Center, said the claim that it raises taxes "on energy" is "debatable, to say the least."
According to FactCheck, oil companies can't pass along higher taxes directly to consumers because prices at the pump are set by the market. More likely, FactCheck said, higher taxes would be borne by stockholders in the form of reduced dividends and capital gains.
Republican economists contend that higher corporate taxes eventually reduce investment, ultimately leading to lower wages for workers and higher prices for customers.
"Either way, it would be more accurate for the ad to accuse Brown of voting for 'higher corporate taxes,' " FactCheck said.
FactCheck also rejected as false the claims about the health-care law.
Justin Barasky, spokesman for the Ohio Democratic Party, said if the ad portrayed Mr. Brown's record accurately, it would help him with voters, not hurt him. "He's eliminating tax breaks on five oil companies. These are tax loopholes that these big oil companies have. It wasn't a tax raise on anyone else," Mr. Barasky said. "What's more important, protecting big oil company tax breaks or lowering the deficit? The Chamber, like Josh Mandel, cares more about protecting big oil companies than lowering the deficit."
He said Mr. Brown isn't hiding from his record, but noted that Mr. Mandel has been largely off-limits to news reporters.
Mr. Barasky also said a photograph of Mr. Brown was doctored to give him a few days' growth of beard.
"We found the original [Associated Press] photo and he doesn't have a beard in it," Mr. Barasky said.
A Chamber of Commerce spokesman declined to reveal the sources of Chamber contributions to pay for its political advertising.
"Everyone knows who the U.S. Chamber of Commerce is -- we represent the interests of the American business community and the American workers those businesses employ," Mr. Fielder said.
He said the point of the ads was to have a conversation about economic issues. The reference to raising energy issues included Mr. Brown's vote in April, 2009, against an amendment to require a 60-vote threshold on any legislation increasing energy taxes. The amendment passed 65-33, and Mr. Brown voted no, Mr. Fielder said.
Mr. Fielder did not respond directly to whether facial hair was added to the picture of Mr. Brown's face.
"If unemployment nationwide is at 9 percent, let's have a conversation about jobs, not shaving practices," Mr. Fielder said.
A request through the Mandel campaign to interview the state treasurer was declined.
Contact Tom Troy at firstname.lastname@example.org or 419-724-6058.