In the USA, "The invention of the
union label is credited to the Carpenter's Eight-Hour League in San Francisco which adopted a stamp in 1869 for use on products produced by mills employing men on the eight (as opposed to ten) hour day. […]
William Green, President of the AFL [(American Federation of Labor)] in 1939 noted that the label's appearance on a product was ‘emblematic of a high standard of living, of tolerable conditions of employment, of those conditions surrounding working men and women which makes for a higher and better standard of living.'"
(Parker, S.,
A brief history of labor symbols,
Labor archives and research center at San Francisco State University, visited 2010-03-16)