Top federal health officials engaged in “serious misconduct” by ignoring concerns of scientists at the Food and Drug Administration and approving for sale unsafe or ineffective medical devices, the scientists have written in a letter to Congress.

The letter to Congress, dated Oct. 14, is part of a growing chorus of dissent from what had long been a tight-lipped agency. In decades past, scientists rarely disagreed publicly with their agency’s decisions, and any concerns they had about important decisions were whispered among veterans.

But increasing scrutiny of the agency on Capitol Hill has coincided with a growing willingness by some scientists to voice their misgivings.

Medical devices include products like cardiac stents, nerve stimulators to relieve depression, imaging equipment and breast implants. It is not clear from the publicly released information which device approvals the scientists questioned.

The letter says that the scientists have documentary evidence that senior agency managers “corrupted the scientific review of medical devices” by ordering experts to change their opinions and conclusions in violation of the law.