People have been worrying about the future of work for 500 years. But at Western Michigan University, those worries are currently being fueled not by advances in technology and automation, but by goats:

A battle is brewing at Western Michigan University this summer between a group of hungry goats and a labor union. The 400-member American Federation of State, County and Municipal Employees has filed a grievance contending that the work the goats are doing in a wooded lot is taking away jobs from laid-off union workers.

That’s from the Battle Creek Enquirer, a local Michigan paper, which reports that Western Michigan is using 20 goats to clear poison ivy and other weeds from about 15 acres of land. Cheryl Roland, a spokeswoman for the university, told the Battle Creek Enquirer that this is the second summer the university has enlisted goat landscapers as a “solution to stay environmentally friendly.” The goats arrived on campus June 2. Nicholas Gooch, a university horticulturist in charge of the project, said they are ahead of schedule in their landscaping efforts.

Reuters/Yuri Gripas Goats graze at the Congressional Cemetery in Washington in April 2015.

The American Federation of State, County, and Municipal Employees alleges that they weren’t notified by Western Michigan about the goats. ”AFSCME takes protecting the jobs of its members very seriously and we have an agreed-upon collective bargaining agreement with Western Michigan,” union president Dennis Moore told the Battle Creek Enquirer. “We expect the contract to be followed, and in circumstances where we feel it’s needed, we file a grievance.” (The union didn’t immediately respond to Quartz’s request for comment.)

Western Michigan is far from the only place to call in goats for groundskeeping duties. Goats have tended to Prospect Park and Brooklyn Bridge Park in New York, the lawns of internet giants Google and Yahoo in Mountain View, and the Congressional Cemetery in Washington, D.C. Proponents of goat-mowing say it’s a sustainable alternative to chemicals and more aggressive landscaping, if also a bit pricier. “Like many organic practices, you are going to have to pay a premium sometimes,” a homeowner in North Carolina told the Wall Street Journal in 2010.

Reuters/Andrew Kelly Nubian goats graze in New York’s Brooklyn Bridge Park in June 2016.

Goat services can be booked on website Rent a Goat, or through Amazon, which highlighted goat grazers when it introduced its “home services” platform in 2015. But as with human workers, goats don’t always get the job done. The city of Salem, Oregon, fired its 75 goat workers in February 2016, complaining that they cost too much, left behind a “heavily fertilized area,” and, ultimately, weren’t particularly selective about what they ate.