The History Channel tells us:
Observed on the first Monday in September, Labor Day pays tribute to the contributions and achievements of American workers. It was created by the labor movement in the late 19th century and became a federal holiday in 1894.
The MDPM team wants to thank all of you who work diligently to keep our great country running. Whether you help us stay healthy or give us smooth roads, whether you’re in agriculture or architecture, your contribution to our society is appreciated. Take this day to relax with your friends and family. The work will still be there tomorrow!