Scarlett Johansson
Scarlett Johansson has had a no-nudity clause in her contract since she was 22. In 2014, she decided to perform nude in Under the Skin. She felt like it was necessary for her character, rather than exploitative like other roles she was offered. She will most likely keep her clothes on for other roles.
Cameron Diaz
Even though her character in There's Something About Mary had a pretty explicit scene that didn't contain nudity, Diaz never intended to go any further than that. She's said that she's really uncomfortable with performing on screen. The first time she was nude in a film was in 2014 for the movie Sex Tape.