I'm a director at a non-profit and some of my programs are currently on pause due to Covid. I've been at my non-profit for 12 years and am now being enlisted to do data entry for fellow directors. I'm in charge of a project that also requires a lot of data entry and I asked my boss if I could enlist colleagues to volunteer one hour per week of their time to help me as I help others. My request was rejected, with my boss saying everyone else is too "swamped." At this point, I think I should threaten to resign if this double standard isn't addressed. What are your thoughts?

Totally unacceptable. You've been there for 12 years and you're at the director level? I understand your current projects may be on pause but there is no reason why others can't also pitch in. However, it doesn't seem like a reason to quit unless there are other issues.
Is there a chance that you were overreacting? You didn’t say that you didn’t have the time for it but rather that if you helped a peer while your project is on pause, they should have to do data entry for you. I think the more reasonable approach would have been to say that you cannot do data entry for them because YOU are too swamped with the work for your own project. Nowhere do you suggest that is the case. Can you clarify the workload better?
OP here: I know the reason I am being asked to do these tasks for others is because my other programs are on pause so they figure "she has time, so let her do it." And yes, it is true that my workload is very light these days. This is more about what I feel are double standards and being treated unfairly in such an obvious way.
@Anonymous Yes, I know for a fact that many other employees have time.
You say it's a double standard -- how? If you have time and they don't, so only you are being asked to do this work, that's not a double standard, that's actually fair -- are you saying it would be fair for you to not do anything even though you have time on your hands and the others don't?
It is fair to ask me to do extra work, but I should be allowed to ask others for help on my projects as well. I just want equal treatment.
@anon123 You're not making sense. It's not extra work if you have plenty of time on your hands.
@MidtownMom Exactly.