There are limits to how long unions can siphon off money from businesses, without facing serious economic repercussions.

The most famous labor union leader, the legendary John L. Lewis, head of the United Mine Workers from 1920 to 1960, secured rising wages and job benefits for the coal miners, far beyond what they could have gotten out of a free market based on supply and demand.

But there is no free lunch.

An economist at the University of Chicago called John L. Lewis “the world’s greatest oil salesman.”

His strikes that interrupted the supply of coal, as well as the resulting wage increases that raised its price, caused many individuals and businesses to switch from using coal to using oil, leading to reduced employment of coal miners. The higher wage rates also led coal companies to replace many miners with machines.

The net result was a huge decline in employment in the coal mining industry, leaving many mining towns virtually ghost towns by the 1960s. There is no free lunch.