I cannot find a specific instance there this book was actually banned or challenged. There are references to it on the internet, but no specifics. As such, I'll just list what I've found and leave it for you to ponder.
Although most books are banned for their sexual behavior or content, Ethan Frome does not contain any of that. There is no obscene language, drug abuse, or even violence. There are, however, other factors that take place in this book that have led to it being banned by several organizations. The main reason would be the attempted suicide. Two lovers decide that since they cannot be together, they cannot be apart either. It portrays the image that the only way to deal with personal issues, is to end your life with no consideration of the affect that it will have on yourself, your friends, or your family.
Another factor for the banning of this book is the infidelity between a married man and another woman. When a man marries a woman, he is taking a vow that he will be with his wife till death do them part. Infidelity is not only ethically wrong, it is also a sin in the Christian faith as it breaks the tenth commandment, “Thou shalt not covet thy neighbor’s house, wife, or possessions”. Many parents do not feel comfortable having their children read a book that has to do with affairs.