A holiday of several meanings, always a legal holiday.
A long-lived pagan custom was to plant an adorned tree on that day to celebrate the return of spring. For the Catholic Church it is the first day of the month of the Virgin. But by far, all over France, it is the succession of the "Workers’ protest Day" (1889-1947) which officially became Labor Day, la fête du travail, in 1947.
The typically French custom on "1er mai "is to offer blossoming lily-of-the-valley to bring luck. For the whole day anyone is allowed to sell lilies-of-the-valley without a vendor’s license. The fragrant can, therefore, be bought at every street corner.