Senior airline pilots in the US are challenging new legislation that allows them to continue flying until age 65, calling the law "unconstitutional and unenforceable."

The Fair Treatment for Experienced Pilots Act, which President George W. Bush signed last month, is not retroactive and does not include any provisions for pilots who turned 60 prior to passage.

In addition to raising the retirement age, the legislation requires older pilots to have a first class medical certificate renewed every six months and to participate in FAA pilot training programs.

Pilots forced to retire before the law went into effect could be rehired but would lose seniority.

"The new law is poorly written and expressly denies carriers the right to treat older pilots fairly, even countermanding prior contractual positions between pilots and their companies," according to George Washington University's Jonathan Turley, who represents the Senior Pilots Coalition.

Turley is seeking an injunction that would void the law.

"In my view, the law can be challenged in federal court on a number of grounds," he said, ticking off a list of antidiscrimination clauses. "Obviously, the best outcome would be a legislative fix. Congress clearly enacted this law with little understanding of its implications or inevitable litigation."