Actress Anne Hathaway. Picture: Reuters

Anne Hathaway has warned people off "fat shaming" her as she is gaining weight for a movie role.

The 35-year-old actress is gaining weight for an upcoming movie role and has already spoken out to blast people she expects will make cruel comments about her figure.

She shared a workout video on Instagram and wrote: "I am gaining weight for a movie role and it is going well. To all the people who are going to fat shame me in the upcoming months, it's not me, it's you.

"PS -- I wanted to set this to Queen's 'Fat Bottomed Girls' but copyright said no.(sic)"

Anne didn't specify which movie she is gaining weight for, but she has a number of projects in the pipeline, including 'The Lifeboat', in which she plays a woman on trial for murder who tells the tale of how she survived a shipwreck at sea on a lifeboat, and as a new mother in 'Live Fast Die Hot'.

The 'Les Miserables' actress - who has two-year-old son Jonathan with husband Adam Shulman - previously spoke about fat shaming and the pressure there is on new mothers to lose the weight they gain during pregnancy.

Speaking a few months after giving birth, she said: There is no shame in gaining weight during pregnancy (or ever). There is no shame if it takes longer than you think it will to lose the weight (if you want to lose it at all). There is no shame in finally breaking down and making your own jean shorts because last summer's are just too dang short for this summer's thighs.

"Bodies change. Bodies grow. Bodies shrink. It's all love (don't let anyone tell you otherwise.).(sic)"