The factory makes uniforms for every major leaguer, from likely Hall of Famers such as Albert Pujols to minor league call-ups like former IronPigs hurler Tyler Cloyd, as well as high-end replicas worn by fans everywhere.

Now a labor dispute that has caught the attention of the Major League Baseball Players Association threatens to disrupt that supply. The textile workers’ three-year contract will expire Friday night. And Pennsylvania Joint Board Workers United, Service Employees ...