Right. McDonalds is of course not one of those Big Corporations.
McJobs aren't going to get outsourced.
However, if illegals get hired there, it damages the labor market for teenagers, many of whom are working part time for extra spending money or for bills.
When I was in High School I has a few friends who worked there, though Micky Ds isn't known to hire illegals, at least over here.
But other jobs that can't be outsourced but can be given to illegal labor thus damaging American Labor or Native Labor are custodial work and many numerious physical intensive on the spot types of work.