It's probably off that he asked subordinates, who may then feel that if they don't support his cause, they will feel the repercussions in some way down the road.
In general though, although I am also weary of being asked to support various causes, I guess it's fine to let everyone know what you're doing, and "here's the link if you wish to donate." How would they know what you're trying to accomplish if you don't tell them? But, as a PP pointed out, multiple requests, cornering people in the lunchroom, FB posts that whine, "There are still people who haven't donated to my cauuuuuuuuse!!!" are off.
Also, it's more likely to inspire giving in me if the cause is not for yourself. "I'm riding my bicycle across Canada to raise money for cancer research" is a lot better than, "Can you donate for my daughter's dance school?" or "We're raising funds for a school trip to Exotic Locale."