Citing family values, Singapore has banned the children’s picture book And Tango Makes Three, the tale of two male Central Park Zoo penguins raising a baby chick together, reports the Guardian. Based on the true story of Roy and Silo, who tried to hatch a rock as if it were an egg, the book is one of three to be banned by the government for its portrayal of nontraditional families.

All copies of Tango, The White Swan Express: A Story About Adoption, and Who’s In My Family: All About Our Families in the country’s 26-branch public library system will be pulped. The book banning has been met with outrage from Singaporeans, who have launched a #FreeMyLibrary social media campaign, created an open letter and petition protesting the decision, and are threatening to boycott the library.

“Parents who object to the content of these books have the option of not borrowing them for their children,” reads the letter. “To withdraw it from circulation is irresponsible and unfair to other library users and parents who may want to teach their children about acceptance, tolerance, and the heterogeneity of family structures.”

Singapore’s National Library Board is defending the unpopular decision in a statement: “NLB’s collection development policy takes special care of our children’s collections to ensure they are age-appropriate. We take a cautious approach, particularly in books and materials for children. NLB’s understanding of family is consistent with that of the Ministry of Social and Family Development and the Ministry of Education.”

The NLB’s decision has received support from the government. “The prevailing norms, which the overwhelming majority of Singaporeans accept, support teaching children about conventional families, but not about alternative, non-traditional families, which is what the books in question are about,” said the country’s minister of communications, Yaacob Ibrahim, in a statement.

“Societies are never static, and will change over time. But NLB’s approach is to reflect existing social norms, and not to challenge or seek to change them,” he added.

The authors of And Tango Makes Three, Justin Richardson and Peter Parnell, aren’t surprised by the public outcry over their book’s banning, with Richardson telling the New York Post: “Public attitudes are changing, and the government in Singapore is underestimating its people.”