Challenged at the Toronto Public Library: 2013.
From the Global News:
Hop on Pop by Dr. Seuss “encourages children to use violence against their fathers” and should be removed from the Toronto Public Library.
That, according to a complaint to the city’s library that wanted to see the book by the beloved children’s author removed from the shelves. The complainant also demanded the Toronto Public Library “issue an apology to fathers in the GTA and pay for damages resulting from the book.”
The library refused, noting the book is “humorous” and “well-loved by children,” it regularly appears on “best of” lists, Dr. Seuss was a Pulitzer Prize winning author and well, the children “are actually told not to hop on pop.”
See the full list here.