In November 1884 was held in Chicago the Fourth Congress of the American Federation of Labor, in which it was proposed that as of 1 May 1886, employers would be forced to respect the 8-hour day and, if not, He would go on strike.
In 1886, the President of the United States, Andrew Johnson, enacted the Law Ingersoll, establishing the 8-hour workday. As this law and labor unions United States was not met mobilized. When the day came, the workers were organized and productive paralyzed the country with more than five thousand strikes.

The most famous episode of this struggle was the unfortunate incident of May 1886 Haymarket Square in Chicago: during a demonstration against the brutal suppression of a recent strike a bomb killed several policemen. But could never find out who was responsible for this attack, four anarchist leaders were accused, summarily tried and executed.
In July 1889, the Second International instituted the "International Workers Day" to perpetuate the memory of the events of May 1886 in Chicago. This claim was undertaken by American workers and immediately adopted and promoted by the International Workers' Association, which became common demand of the working class around the world.
The Paris Congress of the Second International agreed to hold the "Labor Day" on May 1 of each year.

Since 1890, political parties and integrated in the International unions have led demonstrations by workers in various countries on request of the 8-hour day as a sign of fraternity and the international proletariat.

This vindictive and workers' struggle origin is associated with 1 May, the celebration has gone through many ups and downs according to the country and its political regime. Today, almost all democratic countries celebrate it, while unions call for demonstrations and samples perform brotherhood.
In 1954, the Catholic Church, under the leadership of Pius XII, tacitly supported this proletarian day, declaring that day as feast of St. Joseph the Worker.
During the twentieth century, progress were increasing labor laws for workers, to grant rights of respect, remuneration and social protection.

In Argentina, between social laws they may be mentioned: the 4661 law of Sunday rest; 9688 law, which establishes the obligation to compensate accidents and occupational diseases although there is no guilt employer; Law 11,544, which limits the workday to 8 hours and the "Law of dismissal", which deals with the notice and the corresponding compensation.
In our country on May 1 is a national holiday by Law 21329 National holidays and nonworking days.