A true story of two male penguins that raised a baby together is one of the most controversial books in the library, according to the American Library Association (ALA)'s Office for Intellectual Freedom.
"And Tango Makes Three" is third on the list of books that receives the most complaints from library patrons.
The children's book—written by Peter Parnell and Justin Richardson— tells the story of Roy and Silo. The male penguins drew national attention in 2004 after being featured in a New York Times article for performing mating rituals and attempting to hatch a rock.
Eventually, the pair was given an egg that could not be hatched by its parents, and successfully incubated and cared for the chick. Their daughter was named Tango, and went on to have a same-sex relationship of her own.
"And Tango Makes Three" was published in 2005, and was heavily criticised by religious and conservative groups. The authors were accused of promoting a homosexual agenda to children—a claim the men strongly denied.
"We wrote the book to help parents teach children about same-sex parent families," Richardson told the New York Times. "It's no more an argument in favour of human gay relationships than it is a call for children to swallow their fish whole or sleep on rocks."
In the story, Roy and Silo broke up shortly after they became famous, and Silo mated with a female partner. Roy reportedly joined a group of single male penguins.
In addition to the penguin love story, Toni Morrison's "The Bluest Eye," Khaled Hosseini's "The Kite Runner," and "A Stolen Life," by Jaycee Dugard appear on the ALA's complaint list.
The book that received the most complaints in 2014 was "The Absolutely True Diary of a Part-Time Indian" by Sherman Alexie, followed by Marjane Satrapi's "Persepolis."
