In its report Financing Nature in an Age of Austerity, the RSPB suggested funding nature conservation through "environmental taxes" on peat, fertiliser and pesticides.
Briercliffe said: "The RSPB makes selective reference to Defra's peat monitoring project, but no mention of the separate Defra reports into the availability of alternative products and the costs of peat reduction to the industry. The transition would patently not be smooth if you take those reports into account."
He said the report failed to identify where alternative products would come from, adding: "The introduction of a peat tax would do little more than increase costs for manufacturers and consumers at a time when we should be looking to stimulate the economy."
RSPB sustainable development policy officer Olly Watts, who sits on the GMA, said: "The idea of a peat tax has been around for a long time and Defra has been considering fiscal measures.
"We all know that we are in a time of austerity and nature conservation funding is going to be cut, so we are trying to help the Government find ways to help this."
The report emerged in the same week that industry representatives met with Defra minister Richard Benyon to discuss the speed that peat reduction could be achieved.
Briercliffe said: "It was encouraging to hear the minister wanting to find out about the challenges presented by peat reduction. He was pleased by our approach and has agreed to give serious consideration to the industry's concerns."
Horticultural Development Company chairman Neil Bragg said: "The meeting provided a useful opportunity to detail some of the real financial and technical challenges that growers face."