Mac Barnett, the children’s author and national ambassador for young people’s literature, is under fire for remarks in his new book, including a line in which he says that the vast majority of children’s books are “crud,” Publishers Weekly reports.

In Make Believe: On Telling Stories to Children, his first book for adults, Barnett references a statement made by SFF author Theodore Sturgeon in the 1950s: “Sure, 90% of science fiction is crud. That’s because 90% of everything is crud.”

“I have a nagging fear that children’s literature suffers from a slightly higher crud percentage than literature as a whole,” Barnett writes in his book, published Tuesday by Little, Brown. “So I now offer Barnett’s Addendum to Sturgeon’s Law: Maybe more like 94.7 percent of kids’ books are crud.”

Children’s authors and librarians who objected to the passage signed an online petition addressed to the Library of Congress and Every Child a Reader, sponsors of the national ambassador for young people’s literature position. “In a climate where book banning has reached unprecedented numbers…the devastating impact of these words by the National Ambassador of Young People’s Literature cannot be underestimated. The language of this quote arms book banners with an easy script to further attack books already targeted for bans and expands censorship far beyond the current scope,” reads the petition in part. More than 400 people had signed it as of Friday afternoon.

Barnett responded to the controversy in a statement, saying, “First of all, I want to acknowledge the passage I wrote is hurtful, especially to people who work hard making books for kids. I understand why people are upset and feel betrayed. In trying to make a point, I got hyperbolic and glib. I was wrong. I’m truly sorry.”

The position of national ambassador for young people’s literature was created in 2008 to “raise national awareness of the importance of young people’s literature as it relates to lifelong literacy, education, and the development and betterment of the lives of young people.” Previous ambassadors include Gene Luen Yang, Jacqueline Woodson, Jason Reynolds, and Meg Medina.

Michael Schaub is a contributing writer.