The American Civil Liberties Union is calling for an independent investigation into conditions at Ohio's super-maximum security prison amid a long-running hunger strike.

The protest at the Ohio State Penitentiary in Youngstown began March 19 to draw attention to recreation and programming restrictions, including a ban on religious gatherings, imposed after an assault on a corrections officer. A prisons department spokesman couldn't immediately say how many inmates were continuing to refuse meals Monday.

The ACLU detailed its concerns in letters to state prisons director Gary Mohr and to the head of the Legislature's oversight panel. The group cites a 2005 U.S. Supreme Court ruling that upheld the due process rights of supermax prisoners, who are held in their cells for up to 23 hours a day.