KALAMAZOO, Mich. (AP) — A union has filed a grievance in response to Western Michigan University’s hiring of goats to clear 15 acres (6.07 hectares) of woodland on campus.

Kathi Babbit is the chief steward of the American Federation of State, County and Municipal Employees local union. Babbit wrote in a July newsletter that the grievance had been filed in relation to subcontracting and the unreported use of goats, the Kalamazoo Gazette reported.

The university hired the team of goats after a half-acre trial run last year. Officials of goat rental company Munchers on Hooves said the animal consumes 3 to 5 pounds (1.36 to 2.27 kilograms) of vegetation per day and leaves behind natural fertilizer.

University spokeswoman Cheryl Roland said she can’t make a detailed comment about the union’s decision because the university has a process underway for addressing the grievance. But she said that no school workers have been laid off by the goat project.

“This stuff is so thick,” said Munchers co-owner Gina Fickle of the woodland. She said that human laborers can always come in to finish the work after the goats clear up to 5 feet (1.5 meters) above the ground.

“Goats aren’t there taking work away from anybody, they’re making it safer for people,” Fickle said.

Roland said that the goats are a chemical-free option to clear areas that are problems for humans to remove. She also said the goats are a cost-effective way to get rid of poison ivy and invasive species.

University Horticulturist Nicholas Gooch said that the school hasn’t received any complaints about the goats other than the union.

“We have been very happy with the progress, impact and PR generated from this project from both the campus community and the community as a whole,” he said. “There have been no complaints of any nature prior to the news of this union ordeal.”

According to Roland, the goats are expected to be on campus until about a week before fall classes begin.