The multi-award winning singer told his fans that "beautiful Venice is indeed sinking, but not as fast as the boorishly bigoted Brugnaro."
John, 68, who has two children with his partner David Furnish, used his Instagram page to share his alarm and frustration at Mayor Luigi Brugnaro's "divisive" move.
The leader of the Italian city reportedly banned a total of 49 books featuring same-sex couples from schools, fulfilling one of his campaign promises.
Books banned include a French book titled "Jean Has Two Mums", a story of a wolf family where the cub has two mothers.
"And in the opposing corner we have Luigi Brugnaro, the extremely silly looking mayor of Venice. He's stupidly chosen to politicise children's books by banning titles that touch on same sex families living happily ever after...
"So instead of encouraging a world based on inclusiveness, tolerance and love, he's championing a future society that's divisive and fosters ignorance... Beautiful Venice is indeed sinking, but not as fast as the boorishly bigoted Brugnaro.