The labour day

The labour day was created after a movement made by workers on the Chicago streets (1886). The timetable wasn't always as good as it is nowadays, people had to work 16 hours so they thought 16 hours was too much and they wanted it cut to half. Thousands of people have participated in that movement, which created strikes on a large numbers of works.
This revolt was known as the revolt of Haymarket.

Three years later, in paris, Raymond Lavigne, decided to convoke an anual movement to fight against the 16 hours of timetable - the chosen date was May 1st. 
There was a revolt every year, so after more than 30 years of movements, the French senate ratified the 8 hours timetable and proclaimed the May 1st as a national holiday. Since then, other countries adopted the same national holiday and the same timetable.


Labour day in Portugal

As always, Portugal is one of the last countries to accept what's good to the population and only after the fall of the 'New State' the Labour day started to be celebrated.

http://pt.wikipedia.org/wiki/Dia_do_Trabalhador