Normally, labor resources of equal potential productivity flow from low-wage employment to high-wage employment. Why does that not happen to close the union wage advantage? Contrast the voice...

Normally, labor resources of equal potential productivity flow from low-wage employment to high-wage employment. Why does that not happen to close the union wage advantage? Contrast the voice mechanism and the exit mechanism for communicating dissatisfaction. In what two ways do labor unions reduce labor turnover? How might such reductions increase productivity?