Chelsea Supporters Trust says fans have "significant concerns" about the club's future in a lengthy letter to co-owners Todd Boehly and Behdad Eghbali.
It says feeling among fans is at its lowest since the early 1980s and is close to "irreversible toxicity".
Despite a record outlay on players since the new owners took over in 2022, Chelsea are 11th in the Premier League.
"The current mood amongst supporters is critically low and cannot be ignored," CST's letter said.
"The feeling that the club has become a 'laughing stock', both on and off the pitch, is growing.