The animals face a growing threat as the sheer number of horses taken from the rangelands and held in captivity by the Bureau of Land Management threatens to overwhelm the department's budget.
The 30,000 horses and burros held in facilities represent roughly the same number that still wander free on the US western rangelands.
House Natural Resources Committee chairman Nick Rahall (D-WV) and Subcommittee on National Parks, Forests and Public Lands chairman Raul Grijalva (D-AZ) have introduced legislation to protect the animals.
"It is unacceptable for wild horses to be slaughtered without any regard for the general health, well-being, and conservation of these iconic animals that embody the spirit of our American West," Rahall said.
"Introduction of this legislation will ensure the continued presence of those wild horses that make their homes on public lands."
"Our wild horses are being harmed by antiquated policies," added Grijalva. "These policies must be updated to reflect Americans' desire to see these horses protected. We must not lose these majestic icons of the West."
In 1971, the Congress adopted the Wild Free-Roaming Horse and Burro Act which stated that wild horses were an "an integral part of the natural system of the public lands". It set out to protect wild horses from "capture, branding, harassment, or death."
Since then, the BLM, charged with management of the animals on public lands, has allowed for the general public to adopt wild horses that have been captured when their population becomes excessive.
Last summer, the BLM announced that pressure on funding and facilities meant future options may require euthanising of some animals and adoption of others "without limitation" - a move that horse supporters said would open the door to slaughter buyers.
The legislation introduced by Rahal and Grijalva, entitled The Restoring Our American Mustangs (ROAM) Act, would amend the landmark 1971 Act to implement changes suggested in a recent report on the BLM by the Government Accountability Office (GAO), which revealed several problems with the BLM's wild horse and burro programme.
The bill would:
"I am committed to working with my colleagues in the Congress and other stakeholders to correct course and present BLM with a viable management alternative."