The Tennessee Valley Authority stands by its relationship with a contractor accused of undermining safety precautions and sickening workers during the cleanup of a massive coal ash spill.

TVA President and CEO Bill Johnson said in a letter this week that, to TVA’s knowledge, Jacobs Engineering Group had no “history of safety lawsuits or test tampering.”

Johnson also claimed TVA is unaware of mishandled complaints to the utility.

He was responding to a February letter from U.S. Reps. Tim Burchett and Steve Cohen, who asked several probing questions, including what TVA knew about the Jacobs’ safety record, and how the utility responded to workers’ health complaints.

A lawsuit claims Jacobs’ negligence caused the deaths of more than 40 workers and the illness of more than 400 others.