Fifty Shades of Grey fans have expressed disappointment at the announcement that Dakota Johnson and Charlie Hunnam have been cast as the leads in the film version of E.L.James' best-selling erotic novel Fifty Shades of Grey.

An online petition against the casting of the movie has garnered over 40,000 signatures. The petition on states, "We want Matt Bomer and Alexis Bledel as Christian Grey and Anastasia Steele in 50 Shades."

"Matt Bomer is the PERFECT DESCRIPTION OF CHRISTIAN GREY AND ALEXIS BLEDEL IS THE PERFECT ACTRESS TO REPRESENT ANASTASIA STEELE and if THEY ARE NOT, NOBODY WILL BE And I read the whole trilogy and I can assure that Matt is the perfect actor for this movie and Alexis too. So please PLEASE, all of the GREYsessed and Bomerettes in the world NEED those actors. They always will be for us the Christian Grey and Anastasia Steele. WE CAN DO ANYTHING GUYS, ANYTHING," the petition read.

Film's producer Dana Brunetti had taken to Twitter soon after the cast announcement.

"There is a lot that goes into casting that isn't just looks. Talent, availability, their desire to do it, chemistry with other actor, etc," he wrote, adding, "So if your favorite wasn't cast, then it is most likely due to something on that list. Keep that in mind while hating and keep perspective."

It was previously revealed that the film will release in the United States on 1 July next year. British visual artist and filmmaker Sam Taylor-Johnson will be directing a script written Kelly Marcel. Along with Brunetti, Michael De Luca (producers of Oscar-winning The Social Network) will work behind the scenes.