Usually upper management aren’t unionized, I suppose that is true for the SES folks? They shouldn’t be if they are, so shouldn’t be a problem to cut.
I think they are still under civil service rules so almost as good as being in a union. I know when Carter set up the SES program they supposed to be under far less civil service protections. I am sure in the past 40 years those “protections” have crept back in.