Sender of the letter said he was in touch with some Naxal groups, and demanded that Tukaram Mundhe roll back the hike in the rates of a monthly pass scheme for senior citizens.
He will face dire consequences if the hike was not reversed, the letter said.
"A hand-written letter in Marathi has been received by CMD. The letter has been sent from Sukhsagar area and we have registered a non-cognisable offence. Probe is on," said senior police inspector Faruk Kazi.
The sender, who identified himself as 'Bhujangrao Mohite-Patil', claimed that he was writing on behalf of a senior citizens forum.
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)