The Texas Civil Rights Project filed the lawsuit this week in Galveston Federal Court. It's on behalf of four men who died at prisons in Rusk and Palestine in 2011 and 2012.
Scott Medlock directs the prisoners' rights program at the Civil Rights Project. He says the four men took medication for various conditions that made them more susceptible to dying of heat stroke.
"The apparent temperatures — the heat index and the humidity — indoors at these prisons routinely gets into the 130-degree range."
The lawsuit alleges prison officials were negligent. It seeks unspecified monetary damages for the prisoners' families.
Medlock also wants the Department of Criminal Justice to expand the use of air conditioning in its prisons.
"And that doesn't necessarily mean air conditioning all of the facilities. That just means that for the people who are the sickest of the sick — these people like our clients — that you need to put them in a place where they can get some air conditioning during the day."
The Department of Criminal Justice is not directly commenting on the lawsuit. But they did state prison staffers are trained to pay special attention to prisoners with medical conditions that make them more fragile in the heat.
The TDCJ says installing more air conditioners in prisons would be too expensive.