The amendment, sponsored by liberal Senator Paul Wellstone (D-MN) sought to limit the spending of groups like the National Rifle Association and the National Organization of Women.
Wellstone said his provision was needed to close a loophole in the McCain-Feingold bill that would keep corporations and unions from paying for attack ads in the final 60 days of an election but would allow nonprofit groups to place an identical ad.
Many senators and legal experts expect the Supreme Court to rule that the regulation violates the First Amendment. Several opponents of the McCain-Feingold proposal backed the amendment, hoping it would lead to a constitutional challenge to the entire law.
The final proposal passed the Senate by a narrow 51 to 46 vote.
Senator McCain said last night the passage of the amendment made it more important to defeat a proposal expected later this week that would nullify the entire legislation if the courts found just one part of it unconstitutional, dubbed nonseverability.
Senator Feingold called the amendment a possible “bill killer” and also expressed regret that many Democrats had backed the Wellstone amendment.
“This [vote] raised the stakes for everyone,” he said last night. “It’s unfortunate a number of Democrats couldn’t see what they were doing.”