OKLAHOMA CITY - Inside a 20-page letter sent to Oklahoma’s Department of Corrections, lawyers from several chapters of the American Civil Liberties Union and the Prison Law Offices accused Oklahoma's infamous death row, called H-Unit, of violating the religious and civil rights of inmates.

The activist groups said they spent months interviewing death row inmates who are kept in nearly constant solitary confinement. The cells "constitute a dim underground bunker;" the letter reads. "There are no windows to the outside world from the cells and thus no natural light or air.” One inmate compared it to being "buried alive."

According to the letter, the conditions of solitary confinement violate the 8th amendment and no longer reflect modern prison practices.

Lawyers also said inmates are denied religious rights by being prevented access to worship in groups, which is required by some religions including certain denominations of Christianity.

The accusations come as state prisons are working to reduce Oklahoma's record setting incarceration rates and as it struggles to reinstitute the death penalty using nitrogen gas, an untested, first of its kind method. 47 men still await death on Oklahoma’s death row while executions remain on hold.

When asked, a DOC official said they didn't have much to say only that the department's Interim Director Scott Crow was aware of the letter and it was being reviewed by department officials.

In the end the groups are asking the DOC to work with them without a court order but say they are "ready to fully litigate this matter in federal court."