We're used to seeing age restrictions on films and computer games, but now there are plans to put age ratings on BOOKS.
From next year, some publishers are planning to put age labels on the covers of kids' books.
But a row's broken out because lots of top authors, including Philip Pullman and Jacqueline Wilson, thinks it's a bad idea.
So Newsround's Laura went to a school to find out what kids think about it.
Books in the scheme will be divided into five age levels; 5+, 7+, 9+, 11+ and 13+.
But hundreds of authors have signed an online petition, because they think kids will be afraid to try books for older kids, and get teased if they read books for younger ages.
Laura asked kids what they think
To find out if having an age limit would make any difference, Laura showed groups of kids in two separate classrooms a book, and asked them if they'd like to read it.
Laura showed both groups the same book, but with one difference.
One copy had an age restriction label on it, and the other one didn't.
She found that almost the same number of children in each of the classes said they'd like to read it.
So having an age sticker on the cover didn't really make any difference at all to these children.