Federal labor officials are giving Amazon employees in Alabama a second shot at forming a union, and their coworkers in Staten Island are seeking clearance to hold a vote. Americans, more confident of their employment prospects, are leaving their jobs in record numbers, with much of the activity in low-wage industries like hospitality. Employers, having taken note, are combatting high quit rates and staff shortages by raising pay at the bottom of the wage scale. Also fueling the hikes has been a series of increases in state minimum wages, including automatic annual cost-of-living increases in a growing number of states. Various economists, using different data sources, have reached a similar conclusion about these recent developments: pay for low-income workers –…