The letter, dated June 4, 2015 had asked the civic body to give a reply within seven days from receipt, a CBI source told PTI.
This was the first time that any civic body was being questioned by the CBI in the investigation process of the Saradha case.
KMC Mayor Sovan Chatterjee, when contacted, said the civic body did not receive any such letter so far.
"Till date no such letter was received by me. Some scribes showed the letter to me, which was addressed to the chief manager (license) of the KMC," Chatterjee said.