In a statement, CBS called the proposal a "sham, a public relations vehicle designed to distract from the fact that Time Warner Cable is not negotiating in good faith."
"Anyone familiar with the entertainment business knows that the economics and structure of the cable industry doesn't work that way and isn't likely to for quite some time. In short, this was an empty gesture from a company that is expert at them," CBS said.
Sen. John McCain (R-Ariz.) is pushing legislation that would pressure all TV companies to offer their channels a la carte, but the bill has yet to gain momentum on Capitol Hill.
In his letter, Britt also blasted CBS for cutting off access to its online content for Time Warner Cable broadband subscribers.
"Regardless of the other issues between us, it is surely beyond the pale for you to subject these Internet customers to blocking of content that is made available for free to all others," the Time Warner executive wrote.
He noted that the Internet blackout affects customers in cities that still carry CBS and who do not even subscribe to Time Warner for TV service.
Britt accused CBS of "plainly flouting" its obligation to use the airwaves in the interest of the public.
—Updated at 6:22 p.m.