The nation's leading psychologists' association has voted to ban its members from taking part in interrogations at the prison at Guantanamo Bay, Cuba, and other military detention sites where it believes international law is being violated.

The ban means those who are American Psychological Association members can't assist the U.S. military at these sites. They can only work there for humanitarian purposes or with non-governmental groups, according to Stephen Soldz, a Boston psychologist. Soldz is founder of an ethics coalition that has long supported the ban.

"This is a repudiation by the membership of a policy that has been doggedly pursued by APA leadership for year after year," Soldz said last week. "The membership has now spoken and it's now incumbent upon APA to immediately implement this."

The new policy should take effect at the association's next annual meeting in August 2009. However, its council likely will discuss whether to act sooner, said spokeswoman Rhea Farberman.

The interrogation ban brings the psychologists more in line with the American Medical Association and American Psychiatric Association. In 2005, the psychologists association adopted a position that said, for national security purposes, it was ethical to act as consultants for interrogation and information-gathering.

Psychologists have been involved in decisions that approve of coercion methods, including "taking away comfort items like clothes and toilet paper from detainees" to help extract information from them, Soldz said.

He said that some even declined to diagnose post-traumatic stress in detainees because that would suggest detainees had been abused or harmed while in custody.

The group has no real power to enforce its new policy, although its council is expected to discuss whether to recommend the ban become part of its ethics code.

That would mean a violator's membership could be revoked, Farberman said,

Yale University psychologist Alan Kazdin, the group's president, said the policy "will have teeth."

"The organization will be disseminating our position to Congress and to other leaders and make it very clear what psychologists cannot do as part of our policy," he said.