On September 5 , 1882 the first Labor Day parade was held in New York City. By 1886 it became a national event and in 1894 it was made a Federal Holiday. In 1888 labor organizers had called for a general strike on May 1st and in unity countries all around the world recognized the date. Therefore Labor Day in the United States is in September but around the rest of the world it is May 1st even though it was inspired by labor in the United States.
(The Great Courses – Turning Points in American History)