OMAHA, Neb. (AP) — A federal agency has fined Douglas County for violating child labor laws by letting four teenagers load a wood chipper last summer.

The U.S. Department of Labor issued $3,100 in fines after discovering that four underage employees operated a wood chipper while temporarily working on a maintenance crew for the county engineer. Child labor laws allow only adults to do this.

The Douglas County Board is slated to approve payment of the fines Tuesday.

Construction and maintenance manager Tom McDonald said the permanent employee in charge of the wood chipper didn’t know minors weren’t allowed to load it.

McDonald says a workers’ compensation claim filed after one of the teens bruised a finger prompted the Labor Department’s investigation and subsequent fines.