Unions versus opportunity cost

Labor Day has become a government-sponsored PSA that unions use to take credit for every worker gain and offer unionization as the answer to every worker complaint. Near the top of their annual cornucopia of claims is always that union efforts to raise their workers’ wages raise everyone’s wages. Unfortunately, that claim violates one of the most central aspects of economics—the principle of opportunity cost.
Economics starts from the fact that we live in a world of scarcity. C