The U.S. Bureau of Land Management was given the green light Tuesday to move ahead with a controversial horse roundup in Nevada when a federal appeals court lifted a temporary injunction blocking the gathering of more than 1,700 mustangs.

An animal-rights group, the Colorado-based Cloud Foundation, had sued to stop the roundup. A three-judge panel of the 9th U.S. Circuit Court of Appeals in San Francisco said the group had failed to show it likely could prove during future hearings that the roundup is illegal and that removal of horses from federally protected public rangeland would cause irreparable harm.

Critics said another disappointing loss in federal court suggested Congress may have to pass a new law to protect the mustangs because the Wild Free-Roaming Horse and Burros Act of 1971 doesn’t seem to be enforceable.

“We need a new law,” said Rachel Fazio, a lawyer for the Cloud Foundation who had won the temporary restraining order from a judge on the appellate court based on claims the proposed roundup was illegal.

“I think we really need to establish the fact that these animals need to be protected, need to be maintained unmolested by man. And that we mean it this time,” Fazio told the Associated Press.

BLM spokeswoman Heather Emmons said the roundup that had been scheduled to begin last week would start Wednesday in northeast Nevada near the Utah line — weather permitting — and continue for about six weeks.

“We’ll continue with the gather as we were going to, through the end of August,” she told AP.

BLM argued the agency has a mandate under the federal law to remove “excess” horses to sustain the health of herds, rangelands and wildlife. It said the mustang population in the Triple B complex is five times greater than what the range can support.

The Cloud Foundation argued late Monday that the emergency order should remain in place until the government proves the mustangs are causing ecological damage to the range. They said an unusually wet spring has left most public rangeland in northern Nevada with plenty of water and forage.

Fazio said that at worst, the appellate court should have allowed only a small gather to begin while they make their case that there’s no scientific basis to support the roundup of more than 1,700 horses from a series of federally designated horse management areas that make up the complex.

BLM officials said that while some rangeland was in good condition, that would change come winter and that the size of horse herds will double every five years if unchecked.

They said the delay in the roundup was costing taxpayers $17,000 a day to keep contractors in place, “as well as substantial costs to haul water to keep the horses alive.”

Had the roundup been delayed past Thursday, the agency said it would have had to dismiss the contractors and reschedule the gather.

The federal appeals court still intends to hear the merits of the case. It set an Aug. 12 deadline for the Cloud Foundation to file its formal case appealing U.S. District Judge Howard D. McKibben’s refusal on July 15 to block the roundup.

BLM will have a month to reply before any hearing is set.