HIGHLAND PARK, Texas – Teachers at Highland Park High School are sending permission slips home with student for classic English books amid a backlash from parents over reading assignments that involve sex scenes, foul language, or references to rape, abortion and abuse.

Highland Park teachers recently sent permission slips home with 11^th grade advanced placement English students for three classics that have been taught in American schools for decades: The Adventures of Huckleberry Fin by Mark Twain, The Scarlet Letter by Nathaniel Hawthorne, and A Farewell to Arms by Ernest Hemingway, the Dallas Morning News reports.

The books are in addition to a half-dozen others Highland Park Independent School District officials already require parental permission for. Those books include The Art of Racing in the Rain by Garth Stein, Brave New World by Aldous Huxley, Dracula by Bram Stoker, The Glass Castle by Jeannette Walls, The Picture of Dorian Gray by Oscar Wilde, and The Working Poor: Invisible in America by David K. Shipler, according to the news site.

MORE NEWS: Know These Before Moving From Cyprus To The UK

The recent request for permission slips at the high school are not required by the district, but were issued as a precaution amid controversy in the district over which materials are too mature for students. Parents have complained that some books contain sex scenes, foul language, rape, abortion and abuse they don’t want their children reading, while other parents believe the concerns are overblown.

“They cannot limit what our children learn based on a select few parents deciding that they’re not ok with them,” parent Natalie Davis told NBC. “This has really gotten ridiculous and I’m just sick about it.”

Highland Park High School officials took it upon themselves to require parental permission for all books that have been challenged by parents, as well as any books listed on the American Library Association’s Top 10 Challenged Book List in the last decade.

That list also includes Of Mice and Men by John Steinbeck and The Catcher in the Rye by J.D. Salinger.

Highland Park High School Principal Walter Kelly said he sent the directive to require permission slips to gauge how many parents would opt their children out of the reading assignments. Students who are opted out are given an alternative assignment, NBC reports.

The precautionary permission slips come as district officials review instructional materials, library acquisitions and textbooks to address parental concerns about content. District administrators are expected to present their findings to the school board Dec. 9.

MORE NEWS: How to prepare for face-to-face classes

In the meantime, some parents are frustrated that teachers are now required to request permission for basic reading assignments, and sympathized with teachers caught in the crossfire between district policy and parental concerns.

“It’s a blame game,” Lynn Dickinson, mother of an eighth grade student, told the Morning News. “This is putting it back on the teachers who are already squashed between the parents and the administrators.”

Highland Park ISD Superintendent Dawson Orr noted that district officials did not require the additional parental consent for The Adventures of Huckleberry Fin, The Scarlet Letter, or A Farewell to Arms, but commended teachers for taking an overly cautious approach.

“It’s great that (the teachers) chose to be that cautious, but I really don’t believe that they’d want a system that would really require them to have permission for The Scarlet Letter,” Orr told the Morning News. “That’s not a system that they want. It’s not one that we want for them.”

Orr said a full list of books assigned or recommended to students is posted on the district’s website, which also details potentially objectionable content. The online list, Orr said, provides “one place where everyone can go to understand these are the ones that need permission.”