In a move that could affect hundreds of criminal cases, a 3-year-old law that requires federal prisoners and parolees to provide DNA samples for an FBI database was declared unconstitutional Thursday by a federal appeals court.

A three-judge panel of the 9th U.S. Circuit Court of Appeals ruled that requiring blood samples for the database amounts to an illegal invasion of privacy because they are taken without legal suspicion that the convicts were involved in other crimes.

The court said that was a violation of inmates’ Fourth Amendment rights against illegal searches. The samples “constitute suspicionless searches with the objective of furthering law enforcement purposes,” Judge Stephen Reinhardt said.

The San Francisco-based 9th Circuit is the most liberal and overturned federal appeals court in the country. The court’s three-judge panels are known for several contentious rulings, including one that declared the Pledge of Allegiance unconstitutional in public schools and a decision last month that postponed California’s recall election. That ruling was later overturned by a larger 9th Circuit panel.

The ruling could have a sweeping impact on criminal cases in California and other states.

Blood samples taken from federal prisoners and those on supervised release have been used to convict hundreds of people, on crimes such as murder and rape. It was too early to say whether those convictions would survive, said Monica Knox, a deputy public defender of Los Angeles.

Knox also said the decision, if it survives, could nullify state laws that require the taking of blood from inmates and parolees.

“Most states have similar laws,” Knox said. “This could gut those.”

The court covers Arizona, California, Hawaii, Oregon, Idaho, Washington state, Montana, Nevada and Alaska.

FBI spokesman Paul Bresson said the bureau’s database held roughly 1.4 million genetic profiles, most of which came from prisoners and parolees. The FBI does not track the number of samples in the database that match physical evidence collected from unsolved crimes.

But state Atty. Gen. Bill Lockyer said that has happened in California about 400 times, including one that led to the conviction of a man in the 1993 rape and murder of two San Diego youths.