Reading bans are rising at an alarming rate in prisons across the U.S. according to new PEN America data, and are often less documented than bans in other settings, making it hard to determine the extent of the censorship.

“This is an under-reported area because prisons are generally not visible and are isolated environments,” Moira Marquis, the report’s lead author and senior manager in the prison and justice writing department at PEN, said. “The people making decisions are not publicly elected officials, so there is very little accountability.”

Florida now has the highest number of titles banned behind bars, at 22,825, followed by Texas, with 10,265, according to PEN’s new report Reading Between the Bars. Other states like Kansas, Virginia and New York follow behind.