The law allows candidates to receive larger campaign contributions when their wealthy opponents spend heavily out of their own pockets.

The court said by a 5-4 vote that the law violates the First Amendment.

The law was challenged by Jack Davis, a New York Democrat who has so far spent nearly $4 million of his own money in two losing campaigns for Congress and says he will spend another $3 million this year.

Davis says the provision in 6-year-old campaign finance reforms unfairly rewards his opponents by letting them exceed campaign fundraising limits simply because Davis dipped into personal funds.

Writing for the majority, Justice Samuel Alito said that under the amendment, the vigorous exercise of the right to use personal funds to finance campaign speech produces fundraising advantages for the opponents of wealthy candidates.

Alito said that if the millionaire's amendment raised the contribution limits for all candidates, Davis's challenge to the law "would plainly fail," raising the question of whether Congress could easily fix what the Supreme Court struck down.

The amendment has come into play in relatively few races. Its most prominent beneficiary so far has been Sen. Barack Obama. He was able to attract additional contributions for his Democratic senatorial primary campaign in Illinois because an opponent spent nearly $29 million of his own money.

A co-author of the 2002 campaign finance law, Sen. Russ Feingold, D-Wis., said the Supreme Court decision has no impact on the central component of the reforms, the ban on six-figure political donations to political parties. Feingold co-authored the reforms with Sen. John McCain, the Republican presidential nominee-in-waiting.

Sen. Charles Schumer, D-N.Y., said the court had issued a "confounding decision that takes the First Amendment to an illogical, distorted extreme."

Davis lost in 2004 and 2006 to Republican Rep. Tom Reynolds, who spent more than $5 million in winning re-election two years ago, 51 percent to 49 percent.

Reynolds chose not to solicit increased contributions after Davis triggered the millionaire's amendment by putting at least $350,000 of his own money into the race. Reynolds could have received $6,900 from individual donors, triple the limit otherwise. Reynolds is retiring at the end of this term.

Homeland Security Secretary Michael Chertoff has used authority given to him by Congress in 2005 to ignore environmental and other laws and regulations to move forward with hundreds of miles of fencing in Arizona, California, New Mexico and Texas.

The case rejected by the court involved a two-mile section of fence in the San Pedro Riparian National Conservation Area near Naco, Ariz. The section has since been built.

"I am extremely disappointed in the court's decision," Rep. Bennie Thompson, D-Miss., said. "This waiver will only prolong the department from addressing the real issue: their lack of a comprehensive border security plan."

Thompson chairs the House Homeland Security Committee. He and 13 other House democrats — including six other committee chairs — filed a brief in support of the environmentalists' appeal.

Earlier this year, Chertoff waived more than 30 laws and regulations in an effort to finish building 670 miles of fence along the southwest border. Administration officials have said that invoking the legal waivers — which Congress authorized in 1996 and 2005 laws — will cut through bureaucratic red tape and sidestep environmental laws that currently stand in the way of fence construction.

The justices, by a 7-2 vote, said states can give trial judges discretion to prevent someone from acting as his own lawyer if they are concerned that the trial could turn into a farce.

The decision comes in the case of an Indiana man who was convicted of attempted murder and other charges in 2005 for a shooting six years earlier at an Indianapolis department store.

Ahmad Edwards was initially found to be schizophrenic and suffering from delusions and spent most of the five years after the shooting in state psychiatric facilities. But by 2005, he was judged competent to stand trial.

Edwards asked to represent himself. A judge denied the request because he was concerned that Edwards' trial would not be fair. Edwards, represented by a lawyer, was convicted anyway and sentenced to 30 years in prison.

He appealed, and Indiana courts agreed that his right to represent himself had been violated, citing a U.S. high court decision from 1993. The courts overturned his conviction and ordered a new trial.

The Texas Court of Criminal Appeals on Wednesday ruled that Routier should be allowed to conduct DNA testing on blood stains, flakes of dried blood and hairs found at the crime scene.

Routier's previously appeals to the court had been denied, but state law allows for post-conviction DNA testing in some cases. Routier has maintained that she is innocent of the murders.

Routier was accused in the slayings of the young boys, Damon and Devon, but was only tried and convicted in the death of Damon. She has maintained that an intruder at the family's home killed them.

Cavel International Inc. closed its plant in DeKalb, Ill., last year after a federal appeals court upheld the ban. The company urged the justices to step in to allow the facility to reopen. The court did not comment on its order Monday.

The plant was the last horse slaughterhouse in the United States. About 40,000 to 60,000 horses were there annually, and most of the meat was shipped to be eaten by diners overseas.

Two other U.S. plants, both in Texas, also closed in 2007.