Kent Willis, executive director of the ACLU of Virginia, requested the investigation Tuesday in a letter to the Civil Rights Division of the U.S. Department of Justice.
"We believe that these deaths are symptomatic of ongoing unconstitutionally harsh conditions at the jail," Willis wrote.
The jail lacks air conditioning, and Willis pointed to an article in the Richmond Times-Dispatch last week in which Sheriff C.T. Woody said temperatures inside can reach as high as 120 when it's 100 outside. Woody made the remark in discussing the June 26 heat-exposure death of inmate Grant R. Sleeper, 54.
Another prisoner, 49-year-old Kerry Wayne Bennett, was found dead in his bunk June 30. The cause of Bennett's death has not been determined.
"We believe that the conditions at the Richmond City Jail pose a persistent threat to the health and safety of inmates, as illustrated by the two recent deaths," Willis wrote. "Periodic proposals to improve or replace the jail have repeatedly come to naught. The situation at the jail requires federal intervention."
The sheriff's office had no comment on the letter, Col. Walter Allmon said.
Willis said in a telephone interview that the Justice Department, unlike an individual or a group like the ACLU, has the power to file a lawsuit claiming constitutional rights are being violated without having a specific plaintiff.
"Our first step is to see if the Justice Department is willing to do this," Willis said. "They have the resources and the ability."
Justice Department spokesman Alejandro Miyar confirmed receipt of the letter. "We will review the request to determine what action, if any, is appropriate," he said.
If the department declines to intervene, Willis said, the ACLU will consider alternatives including filing a lawsuit on behalf of an aggrieved inmate. Willis said his organization has received more than 50 complaints about conditions at the jail in the last five years.
"It's been overcrowded for as long as I can remember," Willis said. "Right now we have overcrowding exacerbated by heat."
The jail, built in the 1960s, typically exceeds its 850-inmate capacity by several hundred. And last month was the hottest June on record in Richmond, with high temperatures of at least 95 on 11 days and at least 100 on three days. The heat wave has carried over into July, with highs expected in the upper 90s this week.