Is the ISP model where an IC owns multiple routes?
If it is, then technically the drivers who worked for said IC would be able to unionize under their employer.
Now, would an IC allow this to happen? Heck no! To unionize today you have to jump over such hurtles (the major one not being fired by your employer) it is near impossible in many instances.
But remember folks, according to one person (not me), the 7.4% in America in the private workforce who are unionized are destroying the country. So maybe were better off.