The Sims 4 will be given an adults only rating in Russia, due to restrictions put in place by a controversial child protection law passed in 2010. Russian law 436-FZ restricts content seen to be promoting alcohol and dug use, or "unconventional sexual relationships".
The game will be rated 18+, and therefore "prohibited for children." There's no information on which section of the law The Sims 4 is clashing with, but it seems likely that the game's simulation of same-sex relationships is the reason behind the adult rating.
Law 436-FZ came into the spotlight recently at the Sochi Winter Olympics, where gay athletes were warned that revealing their sexual orientation publicly would be in violation of the law.
The developers are unwilling to edit their game to comply with the ruling. "We have no plans to alter The Sims 4," said spokesperson Deborah Coster to Polygon. "One of the key tenets of The Sims is that it is up to the player to decide how to play the game. We provide the simulation sandbox and player choice and creativity does the rest."