The report said a main complaint of the letter is about the new and rule-influential Strategy Group, made up of the grid's 'big five' teams and, for historic reasons, Williams.
The letter follows hot on the heels of Todt's admission that his plans for a mandatory budget cap for 2015 have been scrapped, due to the sudden withdrawal of support of the powerful Strategy Group teams.
The new group, who receive the lion's share of the commercial revenue distributed by Ecclestone, has replaced the old rule-making technical and sporting working groups.
"We have a situation where we have enriched and empowered five teams and disenfranchised six," Force India's Bob Fernley told the Guardian last month.
"The six disenfranchised teams are worthless."
The smallest teams are now reportedly warning that, unless their complaints are listened to, the grid could dramatically dwindle as the more expensive rules take their toll.
"All the teams have taken the cost increase of the new technology but only five have been enriched because of the disproportionate share of the money coming into F1," Fernley explained.
"It's inevitable that all the smaller teams could fall by the wayside."
Sport Bild said the small teams, arguing that their marginalisation could even be contrary to European competition law, want urgent talks to be held ahead of this weekend's Chinese grand prix in Shanghai.
The report quoted an unnamed Red Bull chief as saying: "The letter is explosive and also justified. We do need to change something, starting with a fairer distribution of money, so that the smaller teams get more of the pie.
"We also need to make the sport more attractive, in order to attract more sponsors," the insider added.