Biotechnology companies are keeping university scientists from fully researching the effectiveness and environmental impact of the industry’s genetically modified crops, according to an unusual complaint issued by a group of those scientists.

“No truly independent research can be legally conducted on many critical questions,” the scientists wrote in a statement submitted to the Environmental Protection Agency. The E.P.A. is seeking public comments for scientific meetings it will hold next week on biotech crops.

The statement will probably give support to critics of biotech crops, like environmental groups, who have long complained that the crops have not been studied thoroughly enough and could have unintended health and environmental consequences.

The researchers, 26 corn-insect specialists, withheld their names because they feared being cut off from research by the companies. But several of them agreed in interviews to have their names used.