The letter said the council as well as Kensington and Chelsea Tenant Management Organisation were told on Thursday (July 27) that there were "reasonable grounds to suspect that each organisation may have committed the offence of corporate manslaughter".
The Metropolitan Police has previously stated that the charge was being looked into following the fire which killed at least 80 people at the 24-storey tower block on June 14.
The letter goes on to say that a senior representative from each corporation will be formally interviewed by Met Police in relation to the fire.
Police had gathered "a huge amount of material" as well as having taken "a large number" of witness statements before making the decision to pursue with the potential charge.
The memo adds that this does not mean that this is the only charge being pursued, or these are the only organisations being investigated and that more may follow.
The letter said: "After an initial assessment of that information, the officer leading the investigation has today notified the Royal Borough of Kensington and Chelsea and the Kensington and Chelsea Tenancy Management Organisation that there are reasonable grounds to suspect that each organisation may have committed the offence of corporate manslaughter under the Corporate Manslaughter and Corporate Homicide Act 2007"
The note ends by saying "this work will continue".
A Metropolitan Police spokesman said: "The Met started an investigation into the cause and spread of the fire at Grenfell Tower on 14 June. Since then we have stated that it is a criminal investigation, considering the full range of offences from corporate manslaughter to regulatory breaches.
"This is a complex and far reaching investigation that by its very nature will take a considerable time to complete.
"The Met has made a commitment to the families who lost loved ones in the fire and survivors that they will be kept updated, as far as we possibly can, as the investigation continues.
"As is routine, we will not give a running commentary on this investigation."
Councillor Elizabeth Campbell, leader of Kensington and Chelsea Council, said: “Our residents deserve answers about the Grenfell Tower fire and the police investigation will provide these.
"We fully support the Metropolitan Police investigation and we will cooperate in every way we can.
"It would not be appropriate to comment further on matters subject to the police investigation.”
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