Sen. Sherrod Brown (D-OH), who has been targeted by the advocacy group co-founded by Karl Rove, on Tuesday decried the nation's flimsy campaign finance laws.

"It's bad enough that billionaires and huge corporations -- that have already too much power in our government, in Congress, the executive branch far too often -- that they already have that power and then they can spend money without disclosure," he said on MSNBC.

The pro-Republican Crossroads GPS has launched a $1.1 million ad campaign against Brown. Because the organization is registered as a "social welfare" organization and not a political action committee, it is not required to disclose its sources of funding. Brown suspects that oil companies and Wall Street firms are the ones funding the ad campaign against him, but admitted he doesn't know for certain.

"I think groups that are more progressive don't have these resources," he added. "Keep in mind that when the oil industry is spending this kind of money, when their side wins, they get tax breaks, weaker environmental law, anti-labor legislation. There's real incentive for the individual billionaires to get their taxes cut, so they invest, really is an investment to them. They get billions in benefits."

Brown said progressive groups and labor unions "can't compete" with conservative billionaires like the Koch brothers.

Watch video, courtesy of MSNBC, below:

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