> There was disagreement among labor unions at this time about when a holiday celebrating workers should be, with some advocating for continued emphasis of the September march-and-picnic date while others sought the designation of the more politically charged date of May 1. Conservative Democratic President Grover Cleveland was one of those concerned that a labor holiday on May 1 would tend to become a commemoration of the Haymarket affair and would strengthen socialist and anarchist movements that backed the May 1 commemoration around the globe.[19] In 1887, he publicly supported the September Labor Day holiday as a less inflammatory alternative,[20] formally adopting the date as a United States federal holiday through a law that he signed in 1894.[9]

* https://en.wikipedia.org/wiki/Labor_Day#Labor_Day_versus_May...

(Labour Day in Canada has different reasons.)