They also demanded changes to the games' procurement strategy that would strengthen environmental and sustainability commitments.
James Niven, PR and communications manager at Triodos, told Third Sector: "We need to avoid the situation in which green issues are dropped as costs overrun."
The letter comes after a debate two weeks ago on procurement for the games, during which social entrepreneurs said the sector would struggle to win contracts for the Olympics (Third Sector, 24 January).
The letter, which is signed by Daniel Silverstone, chief executive of recycling consultancy London Remade, Sinead McBrearty, deputy chief executive at Social Enterprise London, Charles Middleton, managing director at Triodos, and Peter Melchett, policy director at the Soil Association, says the ODA should detail the quantity of supplies it expects to source from sustainable local businesses and publish its targets for waste, recycling and green energy.
Niven said: "We are looking at opportunities that would come from wider procurement policies."
A spokesman for the ODA said the organisation's procurement policy for the games would be "open, transparent and fair".