SAN FRANCISCO -- An appeals court Thursday dismissed a Libertarian Party activist's legal challenge to federal airport regulations requiring passengers to show identification before they can board planes.

The 9th U.S. Circuit Court of Appeals rejected claims by millionaire John Gilmore, an early employee of Sun Microsystems Inc., that the policy constituted an illegal search and violated his right to travel freely.

After privately reviewing the government's identification policy that was not disclosed in court for security reasons, an unanimous three-judge panel said the policy was not overly intrusive or illegal. Gilmore, the court ruled, could leave the airport if he didn't want to show his ID and had other ways to get around besides air travel.

"We reject Gilmore's right to travel argument because the Constitution does not guarantee the right to travel by any particular form of transportation," Judge Richard Paez wrote.

The court also rejected assertions that the act of showing identification was an illegal search.

Gilmore's lawyer, William Simpich, said if the government wants to enforce regulations, it should disclose them in writing to the public. He said he is weighing whether to appeal the decision.

"I think they don't want to cough it up because they don't want scrutiny," he said. "We think this is designed as a charade and doesn't make anybody safer."

The court rejected that argument, however, saying airport signs and airline workers give adequate notice that providing identification is required to fly.

Justice Department lawyer Joshua Waldman argued that demanding identification "promotes the right to travel by protecting everyone's safety."

Simpich added that taking Amtrak as an alternative to flying is similarly intrusive, because the train service also requires identification.

Gilmore, of San Francisco, made millions as a founding employee of Sun Microsystems Inc. He also is an active member of the Libertarian Party and a co-founder of the Electronic Frontier Foundation, a civil liberties group concerned with Internet privacy issues.

On July 4, 2002, Southwest Airlines employees at Oakland International Airport stopped Gilmore from boarding a flight to Baltimore after he refused to produce an official photo ID. He also refused to allow security personnel to pat him down or to search through his luggage instead as an alternative to providing identification.

Gilmore had a similar experience with United Airlines employees at San Francisco International Airport later that day. Both airlines said they were following federal directives.