April 12
A group of "puddlers" -- craftsmen who manipulated pig iron to create steel -- met in a Pitsburgh bar and formed The Iron City Forge of the Sons of Vulcan. It was the strongest union in the U.S. in the 1870s, later merging with two other unions to form what was to be the forerunner of the United Steel Workers - 1858
Birth of Florence Reece, active in Harlan County, Ky. coal strikes and author of famed labor song “Which Side Are You On?” - 1900
And this: April 12, 1900 - Florence Reece was born. Active in the Harlan County, Kentucky, coal strikes, she was author of the famous labor song “Which Side Are You On?”

April 12, 1900 - The Stonewear and Potters Union No. 8302 was founded in Red Wing, Minn. The Red Wing Stoneware Company produced dinnerware, crocks and decorative pottery from 1877-1967.
The Union Label and Service Trades Department is founded by the American Federation of Labor. Its mission: promote the products and services of union members - 1909
April 12, 1937 - The U.S. Supreme Court, on a 5-4 vote, upheld the Wagner Act in a series of decisions involving five separate cases. The most significant was probably the case involving Jones & Laughlin Steel Co., in which Chief Justice Charles Evans Hughes wrote the majority decision approving the Wagner Act as falling under the Congress’ constitutional power to regulate interstate commerce. The Wagner Act, also known as the National Labor Relations Act, created the structure for collective bargaining in the United States.
Labor history found here:
http://www.unionist.com/today-in-labor-history & here:
http://www.workdayminnesota.org/index.php?history_9_04_12_2011