One of the Environmental Protection Agency's top outside scientific advisers says a high-ranking political official tried to interfere with her congressional testimony.

Internal EPA emails reveal that chief of staff Ryan Jackson told Deborah Swackhamer, chairwoman of the EPA's Board of Scientific Counselors, that he needed to contact her "as soon as possible to get a copy of her testimony and discuss her question period before the Science Committee," according to a report by NBC News.

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Although Schwarckhamer reassured Jackson that she wouldn't "cross the line" by revealing non-public information during her May 23 testimony, this didn't stop Jackson from emailing her one day prior to her appearance in which he said he had read her prepared testimony (even though it was under embargo at the time) and suggested that she stick to the EPA's "talking points."

"It is customary for the office of general counsel and the chief of staff to provide guidance to an EPA employee testifying in front of Congress," said a spokesperson for the EPA to NBC News, "including the importance of providing factual information and to clarify if they are speaking as an individual, rather than on behalf of the agency."

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By contrast, ranking Democrats from the Senate and House of Representatives Science, Space and Technology Committees sent a letter to the EPA's independent inspector general Arthur Elkins claiming that Jackson's emails "were inappropriate and may have violated federal regulations."

"The right to communicate with Congress is guaranteed," they added. "Attempting to interfere with or obstruct the testimony of any individual to the U.S. Congress is a matter that should be taken extremely seriously and we trust that you will conduct a thorough investigation of the matter."