I worked with guys that used to talk about the 60's and early 70's when there were about 20 freight companies in a 10 block area, many had worked for all 20 in the same month, one guy working 3 shifts in the same day(well actually day and a half) as casuals, One of the reasons given was that a few of the companies would not work them if they were full time at another, some that were full time would take vacations to work across the street..........now none of those old docks are freight companies all are either torn down or bricked up doors as warehouses.