from this site: http://csf.colorado.edu/mail/psn/2000/msg00650.html

"May Day is a day when the workers the world over demonstrate their
international solidarity. It originated in the United States over a
hundred years ago and grew out of the struggle for the 8-hour day....

The first May Day was in 1886 as hundreds of thousands of workers across the country paraded for an 8-hour working day. The center of the strike movement was Chicago, where 80,000 workers participated in a general strike and effectively shut down the city........
In 1889 leaders of the organized labor movement in various countries met in Paris for the International Workingmen's Association. They voted to support the 8-hour fight and set up May 1st 1890 for an international 8-hour day struggle. On that day workers all over Europe paraded and demonstrated in show of their international unity for a shorter working day......
Ever since 1890 May Day has been a day when workers celebrate their gains and demonstrate their unity with the working people of all countries in their common fight against all forms of exploitation and oppression........
Sunday, May 1, 1994, marks the 107th celebration of May Day. For many, May
Day conjures up visions of flower-baskets and maypole dancing -- certainly
valid associations, but there is another important meaning of May Day that
is being quickly forgotten. May Day is International Workers' Day, a time
for working-class people around the world to reflect on the struggles and
accomplishments of workers, remember our martyrs, and recognize that our
sweat and blood has built and sustains the societies in which we live. It
is also a day for folks to put aside work and thumb our noses at the Bosses.
May Day is an opportunity to plan for the time when we will no longer be
forced to sell our lives to wage slavery; a time to renew solidarity and
celebrate the working-class.......
if you search for International Workers' Day as i did you can find out more...