Actors Mariana Tosca, Viggo Mortensen and Kevin Nealon will add their names to a letter to US politicians calling for a halt to federal musters.
The signatories, including well over 100 organisations, argue a moratorium is necessary, pending development of a viable long-term strategy for management of wild horses and burros.
"Without a single dissenting vote, the 1971 Wild Free-Roaming Horse and Burro Act was passed by Congress guaranteeing these animals protection from "capture, branding, harassment and death," said Tosca, who appeared in "Christmas in the Clouds".
"With virtually no oversight, the Bureau of Land Management's manoeuvres are methodically cleansing the land of these animals who have become an inconvenience and impediment to the goals of the ranching, gas and oil industries."
Tosca said greed had been placed above the rights of others "to shape policy to fit private agendas".
"Millions of head of cattle are grazing on public ranges - public ranges that were designated for these wild horses and burros on land that belongs to American taxpayers, not to private entities," she said.
Tosca said she believed responsibility for management of wild horses should be moved to another government agency.
"The assault on America's wild horses and burros must be halted until range studies can be performed and a solid plan is established for the management of these magnificent animals."
Mortensen, who appeared in "The Lord of the Rings", "Appaloosa" and "Hidalgo", thanked those who had contacted government representatives on the issue.
"Your efforts have paid off, prompting Congress to strengthen the protections afforded to wild horses and burros in the United States of America [with the passage of HR 1018]."
Kevin Nealon features in the television series "Weeds".