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. The disputes tend to pit agency managers, who often lean toward approving drugs or devices when the data are equivocal, against agency scientists, who want more certain trial results before allowing the products to be sold.

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 most recent dispute is unusual if only for the number of doctors and scientists who signed their names to the May letter. Previous disagreements involved at most a few agency scientists. Mr. Dingell and Representative Bart Stupak, another Michigan Democrat, released the letter sent to Congress on Oct. 14 but blacked out the scientists’ names and some crucial details the scientists did not want disclosed.

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.