Close to 300 books have been banned in 11 school districts across Missouri, according to PEN America, a free-speech nonprofit.
The bans come after a new Missouri law passed in August made distributing "explicit sexual material" to students a crime punishable by up to a year in jail or a $2,000 fine.
The law does not stipulate exceptions for sexual education courses or those that have anthropological or artistic significance.
Some books include "The Children's Bible," "Maus," graphic novel adaptations of Shakespeare and Mark Twain, Margaret Atwood, and historical books on the Holocaust.
The Wentzville School District removed 220 books for an unspecified "review" period, according to PEN America.
"The books that have been swept up in what I can only call a dragnet in schools is truly astonishing," Jonathan Friedman, director of free expression and education programs at PEN America, said during a Wednesday press conference.
Of the banned books, 76 are about art history. One district pulled six educational books on the Holocaust. Many school districts are now pivoting towards comics, such as Batman, X-Men, and The Walking Dead.
Several graphic novels by LGBTQ authors, especially those including autobiographical stories, have been taken out of Missouri schools.
The ban is allegedly based on sexual material that could be harmful to children.
"What's going on in Missouri is emblematic of this moment because similar trends are now on the horizon," said Friedman noting similar laws against sensitive materials in both Utah and Florida schools.
"So, while Missouri is out in front right now, other places are quickly coming behind," he said.
Dozens of authors signed off on an open letter on Wednesday. Some authors include Margaret Atwood, Neil Gaiman, and Lois Lowry.
"Such overzealous book banning is going to do more harm than good. Book bans limit opportunities for students to see themselves in literature and to build empathy for experiences different from their own," read the letter.
"They deprive students of the freedom to read—to think, to imagine, to grow. And photographs and illustrations can be vital to storytelling: a window into the past, a means of reflecting the human condition, a tool for helping reluctant readers engage with literature."