Full details of the deal reached with the Saving America's Mustangs foundation, which Pickens founded to drive her vision of the sanctuary, have yet to be released.
EWA president John Holland released the following statement today on the plan:
"EWA applauds Madeline Pickens' sincere and considerable efforts on behalf of the mustangs in the BLM's long-term holding pens. However, we have serious questions about the details of the plan and how it might be manipulated by the BLM in their all-too-apparent goal of eliminating the free-roaming mustangs of the West.
"If, as originally presented, the Pickens' sanctuary is to be a substitute for the long-term holding facilities into which mustangs presently disappear, it would represent a welcome improvement.
"However, if it is to be used by the BLM to dump the enormous number of horses it is presently gathering (after sterilising them), then the EWA would be totally opposed to the plan.
"Likewise, if the plan presents cost savings to the BLM over their present system, it would allow the agency to devote even more resources to their extensive gather programme.
"Until these factors are completely understood, the EWA cannot determine the plan's long-term effects and repeats its call for a moratorium on new gathers and asks Congress to remove funding for all gathering operations until a complete scientific study of the situation can be accomplished.
"In short, the EWA would not approve of any plan that did not leave the mustangs as a significant and viable part of the ecology of our public lands."
The EWA is an umbrella group representing more than 100 member organisations and hundreds of individuals worldwide. It focuses on the welfare of all equines and the preservation of wild equids.