The U.S. government is making it harder for scientists to speak to their global colleagues and restricting who can attend an upcoming major AIDS conference, a congressman charged on Thursday.

Rep. Henry Waxman said he has a letter showing that the Health and Human Services Department has imposed new limits on who may speak to the World Health Organization.

Under the new policy, WHO must ask HHS for permission to speak to scientists and must allow HHS to choose who will respond.

“This policy is unprecedented. For the first time political appointees will routinely be able to keep the top experts in their field from responding to WHO requests for guidance on international health issues,” the California Democrat wrote in a letter to HHS Secretary Tommy Thompson.

“This is a raw attempt to exert political control over scientists and scientific evidence in the area of international health,” Waxman wrote.

“Under the new policy the administration will be able to refuse to provide any experts whenever it wishes to stall international progress on controversial topics.”

An HHS spokesman was not immediately available for comment.

Waxman also complained that HHS had cut back a list of scientists planning to attend the International AIDS Society conference in Bangkok, Thailand, next month. The conference is considered the premiere meeting for AIDS experts.

Waxman said that 40 presentations scheduled for the conference were withdrawn after HHS decided that only 50 U.S. scientists could attend.

“The scientific community was outraged by this pullback,” he wrote.

“I ask you to rescind this ill-advised policy until it can be adequately reviewed and justified,” Waxman wrote of the restrictions on WHO requests.

He also urged Thompson to review his decision on the Bangkok conference.