The prestige of John Maynard Keynes, as well as the smart design of his plan, made the proposal for an International Clearing Union particularly worthy of interest when it was released. Economists with orthodox views on international adjustment criticised the plan, but less well known criticisms also came from within Keynesian circles. Several economists in J. M. Keynes’ professional milieu provided comments and asked for amendments to the draft plan in order to improve his scheme for the clearing union. This paper analyses the published responses of Ernst F. Schumacher, Thomas Balogh and Michal Kalecki to the Keynes Plan. These authors provide early, radical criticisms of his plan, targeting the sustainability and efficiency of the proposed international monetary reform.