Reuters reports that the voluntary guidelines may also become compulsory if providers do not follow them and also prove their investment in the projects.
Talking to the news agency, Ofgem chief executive Alistair Buchanan said that it is hoped the measures will "shine a light" onto the green products being offered in the UK.
He added: "We want suppliers to stop re-packaging their existing environmental activity as green immediately and to align their marketing with our guidelines by September 2008."
Earlier this month, Ofgem unveiled new proposals to make amendments to the governance of energy industry codes.
The changes to the process are expected to speed up further amendments and strengthen competition in the sector.