Union workers can say a lot while under the protection of American labor law. For example: “Go back to Africa, you bunch of —ing losers!” That was only one of the racial epithets shouted in 2012 by picketing Ohio tire workers at a group of replacement employees, many of them black. When the tire company fired one offender, its decision was overturned by an administrative judge. That ruling was upheld by the National Labor Relations Board in a 2016 decision, Cooper Tire . These kinds of precedents, employers say, put them in a bind between labor law and workplace standards—even...