It will probably get less attention than the court's landmark ruling on the Second Amendment, but another opinion released by the Supreme Court Thursday will have a potentially significant effect on American elections. In a 5-4 decision, the court said that the so-called millionaire's amendment of campaign finance law violates the First Amendment right to free speech.

The "millionaire's amendment" -- a provision of a 2002 campaign finance law -- was an attempt by Congress to level the playing field for candidates facing wealthy opponents. It applies if a candidate for federal office spends more than $350,000 of his or her own money on a campaign. In that case, the opponent is allowed to collect larger contributions from his or her donors than otherwise allowed. The usual cap on donations from one person in a calendar year is $2,300; the law triples that limit when the amendment comes into play.

The amendment was challenged by Jack Davis, a Democrat who ran against Rep. Tom Reynolds, R-N.Y., in 2004 and 2006. Davis used almost $4 million of his own money in those campaigns, and says he'll spend an additional $3 million this year. Davis contended that the law violated his First Amendment right to free speech and the Fifth Amendment's guarantee of equal protection. Because the court ruled in Davis' favor on his First Amendment claim, it did not address the Fifth Amendment question.

Also struck down were disclosure requirements imposed upon the self-financing candidates, who were required by law to file disclosures within 24 hours every time they made -- or became required to make -- an additional expenditure of $10,000 or more using personal funds.

Justice Samuel Alito wrote the majority opinion; he was joined by his fellow members of the court's conservative wing, Chief Justice John Roberts and Justices Antonin Scalia and Clarence Thomas, and by the court's swing vote, Anthony Kennedy. The court's liberal members -- Justices John Paul Stevens, David Souter, Ruth Bader Ginsburg and Stephen Breyer -- all dissented, joining in part an opinion written by Stevens. Ginsburg wrote a separate dissenting opinion in which she was joined by Breyer. (The four liberal justices all joined the majority opinion in part, agreeing with their colleagues that they had jurisdiction to hear the case.)

Explaining the court's decision, Alito wrote, "While [the law] does not impose a cap on a candidate's expenditure of personal funds, it imposes an unprecedented penalty on any candidate who robustly exercises that First Amendment right, requiring him to choose between the right to engage in unfettered political speech and subjection to discriminatory fundraising limitation." Alito also said there was no "compelling state interest" to justify the speech restriction.

In his dissent, Stevens said no violation of the First Amendment's free-speech rights was involved. "Because the Millionaire's Amendment does not impose any burden whatsoever on the self-funding candidate's freedom to speak, it does not violate the First Amendment, and because it does no more than diminish the unequal strength of the self-funding candidate, it does not violate the equal protection component of the Fifth Amendment," Stevens wrote.