Bachchan plays a lawyer in the film, produced by his frequent collaborator, Shoojit Sircar.
"Work getting really tough on PINK... Scenes and the moment... days ahead are filled with apprehension!!" the 73-year-old wrote on Twitter.
Pink is being directed by Bengali filmmaker Aniruddha Roy Chowdhury and also stars Baby actress Taapsee Pannu. It is set for a September 16 release.
Shoojit has teamed up with Bachchan for the third time after their unreleased film Shoebite and last year's hit Piku, which saw Big B bagging the best actor National Award.
Last Updated 31, Mar 2018, 6:37 PM