May Day:

"May Day occurs on May 1 and refers to several public holidays. In many countries, May Day is synonymous with International Workers' Day, or Labour Day, a day of political demonstrations and celebrations organised by the unions, anarchists, and socialist groups. May Day is also a traditional holiday in many cultures."

In the U.K.:
"The May Day bank holiday was created in 1978. In February 2011 the UK Parliament was reported to be considering scrapping the bank holiday associated with May Day, replacing it with a bank holiday in October, possibly co-inciding with Trafalgar Day (celebrated on the 21st October), to create a 'United Kingdom Day'."

So, not a horribly long tradition for a bank holiday, still, a goodly portion of most current UK workers' lives.

"May Day can refer to various labour celebrations conducted on May 1 that commemorate the fight for the eight hour day. May Day in this regard is called International Workers' Day, or Labour Day. The idea for a "workers holiday" began in Australia in 1856; after a Stonemason's victory, April 22nd was "Eight-Hour Day", a public holiday. With the idea having spread around the world, the choice of May 1st became a commemoration by the Second International for the people involved in the 1886 Haymarket affair [a general strike in Chicago which lead to eventual the public hanging of four anarchists.].
...
"Although the commemoration of May Day as International Workers' Day received its inspiration from the United States, the U.S. Congress designated May 1 as Loyalty Day in 1958 due to the day's perceived appropriation by the Soviet Union."

Further, in the U.S.,
"The first Labor Day in the United States was observed on August 26, 1878, in Boston, by the Central Labor Union of New York, the nation's first integrated major trade union. It became a federal holiday in 1894, when, following the deaths of a number of workers at the hands of the U.S. military and U.S. Marshals during the Pullman Strike, President Grover Cleveland put reconciliation with the labor movement as a top political priority. Fearing further conflict, legislation making Labor Day a national holiday was rushed through Congress unanimously and signed into law a mere six days after the end of the strike. The September date originally chosen by the CLU of NY and observed by many of the nation's trade unions for the past several years was selected rather than the more widespread International Workers' Day because Cleveland was concerned that observance of the latter would stir up negative emotions linked to the Haymarket Affair, for which it had been observed to commemorate. All U.S. states, the District of Columbia, and the territories had made it a statutory holiday."

~ Becky in Long Beach
(a red-diaper baby: born on May 1)