(CNN) Opposition groups have reacted swiftly to notice of a Friday deadline after which Federal officials could start removing a herd of horses from the Tonto National Forest in Arizona.

Though it's unlikely they would start immediately, the Feds said that these are stray and escaped horses and that they pose a public hazard. But advocates who oppose the roundup say these horses are part of the last vestige of an estimated half million "wild" horses that used to roam Arizona.

In a notice posted to much controversy last week, the Forest Service said people have until this Friday to claim their "stray" horses, before service officials may begin removing the horses from Salt River in Tonto National Forest.

With that Friday deadline looming, anger at the federal government turned to action -- swift and organized. So much so, that it garnered a response from Arizona Gov. Doug Ducey.

"Feds should leave our free roaming & #wildhorses alone. But if they don't, #AZ will do everything we can to protect them and provide sanctuary," Ducey said in a tweet posted Wednesday afternoon.

Feds should leave our free roaming & #wildhorses alone. But if they don't, #AZ will do everything we can to protect them & provide sanctuary — Doug Ducey (@dougducey) August 5, 2015

The Salt River Wild Horse Management group, an advocacy group committed to preservation of the Salt River herd, has rounded up opposition to the feds. Within two days, a petition posted by the group on Change.org had received over 75,000 signatures. According to Jason Volentine, a reporter for CNN affiliate KPHO/KTVK , about 100 people gathered for a protest on Tuesday and another is planned for Friday night.

"It's so indicative, we believe, of mankind and our government to just say, 'Let's manage this into extinction,' " said Simone Netherlands, president of the group, to KPHO/KTVK.

According to the advocacy group, a century ago, some 500,000 wild horses roamed the Arizona desert. Today, they say the number is down to 500.

But the Forest Service has said the wild herd that once roamed the Tonto National Forest no longer exists. The agency cited a 1974 census that counted only seven horses and a 1993 census which found only two. The service believes the current herd emerged in the early 2000s partially as a result of a 2002 fire that burned several miles of boundary fence and is therefore not genuinely wild.

The horse population in Tonto is thought to be somewhere between 60 and 100.

According to the Forest Service, Tonto is among the most popular "urban" forests in the country, receiving almost 6 million visitors every year.

What is 'wild'?

The Forest Service disputes that the horses are actually wild. The agency said it believes the horses are strays, which were either let loose or escaped into the forest, and that the wild herd which once lived in the national forest no longer exists. The agency said much of the current population appeared after a 2002 fire that destroyed several miles of fencing.

"These horses have come off of other people's property over the years," Tonto National Forest spokesperson Carrie Templin told KPHO/KTVK. "We are trying to return them to their rightful owners."

If the Forest Service decides the horses are strays, then they will be transferred to the Arizona Department of Agriculture following the roundup. In its notice, the Forest Service said the horses would then be sold as livestock at a public auction and remaining horses could be sold in a private sale or possibly destroyed.

The Forest Service views this as a public safety issue. Officials worry that the horses will pose a danger to people on roads and in campsites. They also say that the Forest Service has no authority to manage this herd due to a federal law passed in the 1970s governing the management of wild horses.

Forest officials said that the roundup will not occur immediately after the Friday deadline, but representatives for the Tonto National Forest told KPHO/KTVK only an act of Congress could keep the horses there.

Organized opposition

None of this has quelled the growing outrage that has followed the Forest Service's public notice of its intent to round up the horses.

For the advocates who view the horses as the legacy of a once robust herd of wild horses, the notice was devastating.

The Salt River Wild Horse Management Group has moved to seek an injunction against the Forest Service in federal court. In an interview with CNN, the group's attorney, Bill Miller, said the Forest Service had not fulfilled its legal requirements, including the completion of an environmental impact study. He also said that the group had evidence that the horses were indeed wild. CNN contacted the Forest Service regarding Miller's claims about legal requirements and alleged evidence that the horses are wild on August 5.

In the moments before Netherlands and Miller planned to file the group's suit, Miller said he hoped the court would act quickly and grant him a hearing before the Forest Service's deadline.

"What we can't have them do is round (the horses) up, to auction them or slaughter them," said Miller. "You know we won't stand for that."

Update:

On August 12, Forest Service spokesperson Carrie Templin spoke with CNN. Templin said the agency had yet to begin the roundup of horses following the August 7 deadline.

Responding to other claims, Templin said the agency continues to view the horses as livestock and that they do not enjoy the protections afforded wild herds. The Forest Service has no need or obligation to complete an environmental impact study, she said.

The agency was coordinating with state officials and the Arizona Congressional delegation to find a workable solution, Templin said. As of now, the Forest Service has no roundup scheduled.