It was a close vote, but the Supreme Court today struck down a key provision of the McCain-Feingold law:

WASHINGTON — The Supreme Court loosened restrictions Monday on corporate- and union-funded television ads that air close to elections, weakening a key provision of a landmark campaign finance law.

The court, split 5-4, upheld an appeals court ruling that an anti-abortion group should have been allowed to air ads during the final two months before the 2004 elections. The law unreasonably limits speech and violates the group’s First Amendment rights, the court said.

The decision could lead to a bigger role for corporations, unions and other interest groups in the 2008 presidential and congressional elections.

The case involved advertisements that Wisconsin Right to Life was prevented from broadcasting. The ads asked voters to contact the state’s two senators, Democrats Russ Feingold and Herb Kohl, and urge them not to filibuster President Bush’s judicial nominees.

Feingold, a co-author of the campaign finance law, was up for re-election in 2004.

The provision in question was aimed at preventing the airing of issue ads that cast candidates in positive or negative lights while stopping short of explicitly calling for their election or defeat. Sponsors of such ads have contended they are exempt from certain limits on contributions in federal elections.