http://boards.straightdope.com/sdmb/showthread.php?t=659718 http://boards.straightdope.com/sdmb/showthread.php?t=659718 short answer: It depends on the union.

http://boards.straightdope.com/sdmb/showthread.php?t=659718 http://boards.straightdope.com/sdmb/showthread.php?t=659718 short answer: It depends on the union. It does happen in this country.