Washington (CNN) -- Senate Republicans narrowly blocked Democratic campaign finance disclosure legislation in the Senate Tuesday after raising concerns the bill would curb freedom of speech and tilt campaign spending in favor of the Democrats.
A 57-41 vote fell short of the 60 votes needed for the Senate to cut off debate on the measure. Republicans unanimously opposed the measure while Democrats solidly backed it.
Democrats said the legislation -- known as the DISCLOSE Act -- would bring greater transparency to campaign contributions from corporations, labor unions, and other special interests, which were able to ramp up political spending in the wake of the Supreme Court's controversial ruling in Citizens United vs. Federal Election Commission earlier this year.
The bill would require organizations paying for political advertising to disclose the names of their top donors in the ads, similar to what now is required of political candidates for federal office.
Republicans accused Democrats of trying to preserve their majorities in the House and Senate by skewing the rules in the favor of labor unions, trial lawyers, and other Democratic-leaning groups. Democrats denied that was their motive, and made certain changes to the bill last week aimed at satisfying GOP critics.
The Republicans were not mollified.
Democrats "fear the righteous judgment of the American people in this coming election," warned Sen. John Cornyn, R-Texas, who spearheads the Senate Republicans' election effort. "So they're trying to change the rules in the middle of the game to suppress the speech of those who might disagree" with them.
Senate Minority Leader Mitch McConnell, R-Kentucky, slammed the bill as a "partisan effort, pure and simple."
"This bill is about protecting incumbent Democrats from criticism ahead of this November's election," he said. It's an "all-out assault on the First Amendment."
Democrats accused Republicans of going back on their pledge to find a way to add transparency to political giving after the Citizens United ruling. They argued that without the new law, special interests will run roughshod over voters' interests.
"The Supreme Court decision was a true step backwards for this democracy," said Sen. Patty Murray, D-Washington. "It allowed corporations and special interest groups to spend unlimited amounts of their money influencing our democracy and it opens the door wide for foreign corporations to spend their money on elections right here in the United States."
Senate Majority Leader Harry Reid, D-Nevada, said the bill was "about trust and confidence in our democracy." The measure "asks us to put the people before the special interests," he argued. Let in "the sunlight that disinfects our democracy."
Sen. Olympia Snowe, R-Maine, who often votes with Democrats and who has worked on campaign finance legislation in the past, complained Democrats were resorting to "ram and jam" legislating in which Republicans are not invited to help craft bills and are forced to vote against measures they could have supported.
"I know it's good for politics to have a vote, but it isn't good for policy and getting it right," she said.
Sen. Charles Schumer, D-New York, promised that the Democratic leadership will continue to seek ways to overturn or reduce the impact of the high court's Citizens United ruling.
"This is a sad day for our democracy," he said. "This fight will continue."
CNN's Alan Silverleib contributed to this report