In a surprise move, the Supreme Court said it would delay a decision on whether a conservative group's film criticizing Hillary Rodham Clinton ran afoul of campaign finance laws.

Instead, the court scheduled a rare September hearing on whether the law itself raised constitutional problems, and it said it would reexamine a 1990 decision that said restricting corporations from spending money on political candidates did not violate their free speech.

Campaign finance experts said such a move could have a dramatic effect on the 2010 and 2012 elections.

"This has the potential to be a blockbuster," said Michael Toner, a former chairman of the Federal Election Commission.

The court said it would withhold its decision about "Hillary: The Movie" until it received briefings this summer about the larger issues. It will hear arguments Sept. 9.

The court will be without Justice David Souter, who has been one of the most consistent supporters of the McCain-Feingold Act.

The White House and supporters of court nominee Sonia Sotomayor said the September hearing should be additional motivation for the Senate to vote on her confirmation before it adjourns in August.

At issue is a part of the law that forbids corporations, unions and special interest groups from using money from its general treasuries for "any broadcast, cable or satellite communications" that refer to a candidate for federal office within a certain time frame before an election.

In the past, that has meant short campaign ads. But a lower court said the same rule applied to Citizens United's scathing 90-minute movie on Clinton as she ran for president.

Citizens United's attorney said the court should use the case to overturn the corporate spending ban. But the court apparently decided it could not make such decisions without briefings on what would be a bold move.