NEW YORK (AP) — Ahead of Labor Day, unions representing millions across several working-class sectors are threatening to authorize work stoppages in support of the Black Lives Matter movement amid calls for concrete measures that address racial injustice. In a statement first shared with The Associated Press, labor leaders who represent teachers, autoworkers, truck drivers and clerical staff, among others, signaled a willingness Friday to escalate protest tactics to force local and federal lawmakers to take action on policing reform and systemic racism. They said the walkouts, if they were to move forward with them, would last for as long...