The Supreme Court is taking up a key element of the landmark McCain-Feingold campaign finance law in a challenge to the constitutionality of restrictions on pre-election issue ads that mention a candidate by name.

Last year a lower court relaxed the law's restrictions on issue ads that are run by corporations, labor unions and other special interest groups in the final weeks of a campaign.

The court sided with Wisconsin Right to Life, an anti-abortion group that had sought to run ads during the 2004 campaign, asking 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.

But because Feingold was up for re-election, the group could not run the ads in the final stretch of the campaign, under a provision of McCain-Feingold that prohibits interest groups from running corporate-funded radio and TV ads that mention a candidate's name within 30 days of a primary or 60 days of a general election.

In oral arguments before the Supreme Court on Wednesday, Wisconsin Right to Life was to assert that McCain-Feingold unfairly restricts its free-speech rights. In its decision in December, a federal appeals court ruled that groups may mention candidates by name in ads as long as they are trying to influence public policy, rather than sway an election.

The McCain-Feingold provision in question was aimed at preventing the common practice of issues ads that stopped short of calling for the election or defeat of a specific candidate, but that would cast a candidate in a positive or negative light. By doing so, sponsors of such ads had been able to circumvent limits on contributions in federal elections.

Wisconsin Right to Life argues it was not trying to influence an election, but rather rally people to lobby senators on an issue before the Senate.

On the other side of the case is the Federal Election Commission and a group of lawmakers led by Sen. John McCain, the Arizona Republican who co-sponsored the McCain-Feingold law.

They argue that issue ads in the waning days of an election always have some influence on voters, and note that Wisconsin Right to Life's political action committee opposed Feingold's re-election.

In 2003, Sandra Day O'Connor joined the four liberal justices in upholding large portions of McCain-Feingold law. She has since retired and her replacement, Justice Samuel Alito, is considered more conservative.

The court is expected to rule in the case this summer.

The consolidated case is Federal Election Commission v. Wisconsin Right to Life, 06-969, and McCain v. Wisconsin Right to Life, 06-970.