December 20
December 20, 1790 - The first American cotton mill began operation in Pawtucket, Rhode Island.
Delegates to the AFL convention in Salt Lake City endorse a constitutional amendment to give women the right to vote - 1899.
The first group of 15 Filipino plantation workers recruited by the Hawaiian Sugar Planters Association arrive in Hawaii. By 1932 more than 100,000 Filipinos will be working in the fields - 1906
The Occupational Safety and Health Act (OSHA) takes effect today - 1970

Thousands of workers began what was to be a two-day strike of the New York City transit system over retirement, pension and wage issues. The strike violated the state’s Taylor Law; TWU Local 100 President Roger Toussaint was jailed for ten days and the union was fined $2.5 million - 2005
Labor history found here:
http://www.unionist.com/today-in-labor-history & here:
http://www.workdayminnesota.org/index.php?history_9_12_20_2010