On August 1st, 1972, Governor Richard Kneip asked for "compulsory negotiations" to bring an end to a 15-day strike at the Homestake Gold Mine according to the Lead Daily Call. In a news conference, Gov. Kneip requested the assistance of a federal mediator. Between 1,400 and 1,600 people were out of work due to the union backed strike. State officials asserted that the strike was having an adverse effect on the economy of the Lead-Deadwood area and the rest of the Northern Black Hills and even leading miners to seek work elsewhere in the country.
The Homestake Gold Mine was no stranger to tensions between management and labor. In November 1909, the Western Federation of Miners attempted to force Black Hills mines to unionize by refusing to work with non-union miners. Homestake instituted a lockout of all miners, and other area mines followed suit. Before miners were allowed to return to work, the company required them to sign an agreement stating that they would not join a union. This tactic effectively ended mining unions in the Black Hills for the next several decades.
For more about the history of the Homestake Gold Mine and its unions, see this publication from the South Dakota State Historical Society and this article from the Black Hills Knowledge Network Archives.