The Senate will try to end debate on the Disclose Act, S. 3369, early Monday evening, although Republicans indicated they would vote against ending debate, which would prevent it from going forward. Whitehouse said the GOP is opposing the bill despite polls showing that six in 10 Americans support more transparency when it comes to how organizations raise and spend campaign money.

"The organizations paying for many of these ads have patriotic and benign sounding names with words like 'prosperity' and 'freedom' and 'future,' " Whitehouse said. "These names sound harmless, but all too often the ads are actually paid for by secret special interests. Billionaires and wealthy corporations seeking secret special influence in our democracy.

"These special interests have motives," he added. "And if those motives were good for America, if they were welcome to the average American, they wouldn't need and they wouldn't want to keep them secret.

"So we need to ask ourselves a very important question: what are they hiding? Why do they demand secrecy?"

The bill responds to the Supreme Court's Citizens United decision, which Whitehouse called "disastrous" for finding that the government cannot limit campaign spending by these groups.

The Senate failed to advance a similar bill in 2010, and Whitehouse praised the new bill for making it easier for groups to comply. The Democratic bill in 2010 would have required reporting after $600 in campaign spending.

Several other Democrats joined Whitehouse on the floor in favor of the bill, and Democrats were planning to debate the issue even after the evening vote that Republicans are expected to successfully block.

"I believe that the amount of money in American politics today is stealing America's democracy," Sen. John KerryJohn KerryIn Europe, Biden seeks to reassert U.S. climate leadership Climate progressives launch first action against Biden amid growing frustration What US policymakers can glean from Iceland's clean energy evolution MORE (D-Mass.) said. "It is robbing Americans of the right to have the kind of representation and the kind of discussion that Americans deserve."

A few Republicans accused Democrats of setting up a vote they know will fail in order to score political points against the GOP, and accused Democrats of ignoring the pending tax increases that will take place at the start of 2013 without congressional action.