This [1] lays out pretty conclusively that even though the book plays lip service to "federal Service", the entire rest of the book makes clear that it is only military that get the right to vote, not "government workers".
I don't think that is correct at all. I read the book and it was very clear to me that it wasn't just lip service, you could do your federal service in many different ways.
I felt the opposite when I read it, which led me to looking around and finding that essay. It felt like he said you could do any federal service, but no federal service actual existed outside of the military. I personally think this is more of the case of the author intending one thing and writing another. Clearly Heinlein intended for it to be about Federal service, but over and over in the actual details, there just is not a Federal Service. It is only the military. That is my main issue with the book, it proposes one society, but it builds a different one. They tells us you can join Federal Service, but those people don’t exist anywhere in the text. Not current Federal workers or former ones, now citizens.
[1] https://www.nitrosyncretic.com/pdfs/nature_of_fedsvc_1996.pd...