The 70-year-old Bollywood star, who is the brand ambassador of Gujarat Tourism, said the video was made by manipulating a voiceover that he did in 2007 for a campaign.
"Dear all... Fake video circulation... In the year 2007, I did a 'Lead India' campaign..., where we talked of the glorification of the country and India!
"Somebody has made a fake video by using my voice and text of what I spoke in the original, and falsely and mischievously, interspersed it with visuals which indicate a campaign for the promotion of the Hon Chief Minister of Gujarat, Shri Narendra Modi!!," Bachchan wrote on his blogbesides posting several alerts about the video on his official Twitter page.
The veteran actor said that it was "an illegal act, inviting strong action, one that I am appalled by, and one that has no concurrence from me at all."
Bachchan called it a blatant misuse and infringement of the Copyright Act. He said he has brought this to the notice of the concerned authorities and has also asked his digital team to find out its origin "so that we can initiate action against the perpetrator. Infuriated and angered!!."
Modi too has come out in Bachchan's support on Twitter, which was retweeted by the actor.
"Agree with @SrBachchan. The author of the fake video should take action immediately and apologize to Amitabh ji," Modi said in his tweet.
Bachchan also posted his original version along with the fake one. His fans have come out in his support by retweeting his response and demanding a ban on the video.
Gujarat Chief Minister Narendra Modi today sought an apology from the creator of a fake online video, which allegedly used the Bollywood megastar Amitabh Bachchan's voice to praise the BJP strongman.
"The author of the fake video should take action immediately and apologise to Amitabhji", Modi said on micro-blogging site Twitter today in response to Bachchan's demand for action against the person who uploaded it.
Earlier, the 70-year-old actor was furious over the fake video posted on YouTube which gave an impression of him endorsing a campaign promotion for Modi.
"Some body has made a fake video by using my voice and text of what I spoke in the original Lead India campaign and falsely and mischieveously interspersed it with usual, which indicates a campaign promotion of honourable Chief Minister Narendra Modi," an angry Bachchan had tweeted.