The American Civil Liberties Union (ACLU) is alleging that two New Jersey prisons have banned a book on the rise of mass incarceration in the U.S., The Intercept reported Monday.

The ACLU of New Jersey said the prisons have banned “The New Jim Crow: Mass Incarceration in the Age of Colorblindness,” which the group says violates inmates’ First Amendment rights.

“Michelle Alexander’s book chronicles how people of color are not just locked in, but locked out of civic life, and New Jersey has exiled them even further by banning this text specifically for them,” Amol Sinha, ACLU of New Jersey’s executive director, said in a statement.

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The ACLU of New Jersey said it received multiple complaints from inmates and their family members about the book being banned. The group then filed an Open Public Records Act request, and the response showed the book was banned “as a matter of policy,” The Intercept reported.

The New Jersey Department of Corrections did not respond to The Intercept’s request for comment.

Democratic lawmakers last year introduced legislation to encourage states to reduce their prison populations.