The film is based on an Aligarh Muslim University professor, who was suspended for allegedly having gay sex, weeks before his retirement in 2010.
S R Siras was later reinstated after Allahabad High Court revoked the suspension. He died the same year.
"The film is based on many such true incidents which are happening in our country for a long time. Marginalization of people based on religion, caste, gender and sexual orientation is not new. I feel the debate on sexual orientation should be a part of mainstream," Mehta said.
"We all face marginalization for different reasons in a regressive society. Such minorities make a big part of our country. Their wishes should not be cornered," he added.
The untitled film, starring Manoj Bajpayee, 45, as the professor and Rajkummar Rao as a journalist, will mark the beginning of Mehta's production company Karma Pictures.
The director got to know about the incident when a girl, Ishani Banerji, mailed him the story in the beginning of this year. His editor Apurva Asrani is turning writer with the film.
On his decision to cast Manoj, Mehta said he was trying to find a good story to work with the versatile actor.
"My casting director Mukesh Chhabra called Manoj for the role. He phoned me asking why I did not call him directly. He is an old friend. I wanted to work with him for a long time but in a role that he has not done before," he said.
Mehta is collaborating with Rajkummar, 30, for a third time with this film.
"I can't work without Rajkummar. I see him in every film of mine. He is a part of my family now. I always find a character for him. He is a great actor and one of the best in the new generation. I thought it would be interesting to bring two such performers together," said the director.

The director is not worried about any possible backlash on the movie.
"I never think about roadblocks. I think they are in our mind. It is a story that will be told with all honesty and humanity. I was told 'Shahid' (based on slain lawyer and human rights activist Shahid Azmi) will face trouble but it did not. So, I am not worried about that," Mehta said.
Mehta is keen to begin production on the film soon. "Immediately after 'Shahid', I started working on 'CityLights' and it got released within six to eight months. I am fast that way. I want to continue with that pace. I have so many stories. It is a mission to tell those stories," he said.

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