Organized labor's instantaneous support for President Obama's recent proposal to hike the minimum wage doesn't make much sense at first glance. The average private-sector union member—at least one who still has a job—earns $22 an hour according to the Bureau of Labor Statistics. That's a far cry from the current $7.25 per hour federal minimum wage, or the $9 per hour the president has proposed. Altruistic solidarity with lower-paid workers isn't the reason for organized labor's cheerleading, either.

The real reason is that...