Charter—backed by John Malone's Liberty Media—is planning to send the letter to as early as next week, the report said, citing a source with knowledge of the matter.
Charter representatives declined to comment on the planned bid. The bid is reportedly an attempt to gain leverage in future programming discussions with TV networks.
Recent reports, citing sources close to the situation, said Comcast has sought advice on possible regulatory hurdles if it decides to pursue a bid for TWC. Comcast owns NBCUniversal, the parent of CNBC.