The original proposition is a little ambiguous: One root goes to Canada, another one to a worker of the CLU. However, after the Pullman Strike in 1894 involved the death of many workers at hands of the U. S. military (amongst others), the Congress voted in union for a national holiday.
To conclude the history lesson: Why is the 1st May not honored? Back in 1886 a labor demonstration in favor of the eight-hours-week was bombed (to google: Haymarket affair). That's just been around the beginning of May, so there won't be any confusion with the memorial of the bombing and the Labor Day if a long weekend appears in September...
... in order to open the football season, of course! :-) If you might not be into football, many retailing stores will welcome you with open arms, since it's on of the greatest annual SALES-day (next to e. g. taken the Black Friday after Christmas). I really get the point of getting up at 2 am to do my Hollister shopping for half the usual prices...
Just briefly, the vicinity: