The actress slammed US censors for awarding the movie an NC-17 rating, insisting that the rating is due to the fact that the film depicts "unattractive" sex scenes.
"You know, so many of the teen movies will have so much sex and so many people walking around in bikinis and bare-breasted, and that all seems to be okay," Mulligan told Hit Fix.
"And then the minute you show it and it's not funny, and it's not sexy, and it's actually unattractive, then it becomes a problem, which seems so odd."
Shame centres on a sex addict named Brandon (Michael Fassbender) whose life gets more complicated when his younger sister (Carey Mulligan) moves in with him.
Mulligan recently admitted that she was scared to kiss Johnny Depp on screen in the 2009 film Public Enemies.
Shame will be released in the US on December 2, 2011 and in the UK on January 13, 2012.
Watch the trailer for Shame below: