NASHVILLE, Tenn. (AP) — The Tennessee Valley Authority is defending its relationship with a contractor accused of subverting safety precautions and sickening workers during the cleanup of a massive coal ash spill.

In a letter this week, TVA President and CEO Bill Johnson said that to TVA’s knowledge, Jacobs Engineering Group “did not have a history of safety lawsuits or test tampering.” He also said TVA is unaware of complaints to the utility being mishandled.

He was responding to a February letter from U.S. Reps. Tim Burchett and Steve Cohen asking several questions, including what TVA knew about the company’s safety record and how the utility responded to worker health complaints.

A lawsuit claims Jacobs’ negligence is to blame for the deaths of more than 40 workers and illness of more than 400 others.