Senate Republicans have blocked legislation imposing restrictions on political activity by special interest groups.
The vote was 57-41, three votes short of the 60 the bill needed to advance.
Democratic supporters backed by the White House said the legislation was needed to force shadowy interest groups that run millions of dollars worth of campaign attack ads to disclose their donors.
Republicans countered that it was a violation of First Amendment rights of free speech, saying it would have treated some groups differently than others.
The disclosure requirement for ads would have applied to many organizations, but not the National Rifle Association or AARP.
Another test vote on the bill is possible in the future.
This program aired on July 27, 2010. The audio for this program is not available.