Labour Day.

Today I learned: that the American Labor Day celebration in September, rather than in May, has its origins in Canada: http://www.thecanadianencyclopedia.ca/en/article/labour-day/

Wikipedia adds:

The origins of Labour Day in Canada can be traced back to December 1872 when a parade was staged in support of the Toronto Typographical Union's strike for a 58-hour work-week.[5] The Toronto Trades Assembly (TTA) called its 27 unions to demonstrate in support of the Typographical Union who had been on strike since 25 March.[5] George Brown, Canadian politician and editor of the Toronto Globe hit back at his striking employees, pressing police to charge the Typographical Union with "conspiracy."[5] Although the laws criminalising union activity were outdated and had already been abolished in Great Britain, they were still on the books in Canada and police arrested 24 leaders of the Typographical Union. Labour leaders decided to call another similar demonstration on 3 September to protest the arrests. Seven unions marched in Ottawa, prompting a promise by Canadian Prime Minister Sir John A. Macdonald to repeal the "barbarous" anti-union laws.[5] Parliament passed the Trade Union Act on 14 June the following year, and soon all unions were seeking a 54-hour work-week.

The Toronto Trades and Labour Council (successor to the TTA) held similar celebrations every spring. American Peter J. McGuire, co-founder of the American Federation of Labor, was asked to speak at a labour festival in Toronto, Canada on 22 July 1882. Returning to the United States, McGuire and the Knights of Labor organised a similar parade based on the Canadian event on 5 September 1882 in New York City, USA.