A survey of scientists at the Environmental Protection Agency shows that hundreds of scientists are complaining about political interference and pressure from superiors who want to skew their findings.

The survey by the advocacy group Union of Concerned Scientists said more than half of roughly 1,600 EPA staff scientists who responded online to a detailed questionnaire reported they had experienced incidents of political interference in their work.

EPA spokesman Jonathan Shradar attributed some of the discontent to the "passion" scientists have toward their work.

The survey was sent to 5,500 EPA scientists across the country with about 30 percent of them responding.