I work for a large corporation and writing letters of recommendation for employees who are applying to grad school is definitely part of my job.
OP- are you working now? I can’t imagine your boss or someone in a supervisory capacity would resent being asked. It takes 10 minutes. If someone refuses I would take that as a sign that they aren’t comfortable endorsing your overall trustworthiness/work ethic, etc. NOT that they are too busy to write a letter.
I just did an LOR and the university actually sent me a nicely done template- they didn’t want a letter so much as a “fill in the blanks” based on some prompts. It was super easy, and when done, I uploaded it into a confidential application file.