They were frequently dug by coal miners off official tunnels in order to procure additional, free coal for themselves, a practice that causes additional ramifications when fighting mine fires.
The practice has died away in the United States; an American with simple equipment cannot dig enough coal in a day to reach a living wage.
Shortly before the Great Depression, Pennsylvania's anthracite industry collapsed, shutting down collieries and throwing tens of thousands of miners out of work.
[3] Bootleg mines were most frequently created in Upper Silesia during the economic crisis of 1929–1933, and were often the only source of income for entire families.
Due to the non-compliance with health and safety regulations and work performed by unqualified people, it is a very dangerous activity resulting in numerous accidents, including fatalities.