Yes, because their reasons for doing it are reasonable.
If you want to challenge your employers' requirement, then you need to show it is unreasonable. They will argue that it is reasonable. Which it, in fact is.
And their argument will look like this:
A lot of people think "The mask only protects me, so I should be allowed to take my chances. I'll just take myself out of circulation if I get sick."
That is not how COVID-19 works, and is what makes it so insidious.
You are a carrier long before you feel symptoms
It is not uncommon to catch COVID-19 on day 1... have it develop enough that you are infecting other people by day 3 -- and only on day 12 does it sicken you enough for you to detect that you are sick (and self-quarantine etc). So for 9 days, you are a carrier - a "Typhoid Mary", who is not sick but spreads the sickness.
Not only that, some data suggests many people go through the catching - carrier - illness - recovery cycle without even realizing they were ever sick. A study showed 20% of New Yorkers revealed they had COVID-19 antibodies!
The pop notion, of course, is that you are not contagious until you feel seriously sick, and the logic is "therefore I'll just take myself out of circulation at that time". That was never really true, but this tactic really doesn't cut the mustard with COVID. The scientists are clear that if we used that usual tactic, COVID would tear the world apart.
And that's why all the leaders are requiring stay-at-home, social distancing and masks.
The masks serve a vital purpose other than PPE
You are used to masks being used to protect yourself. As you know, they're not that great for that. But this isn't the real value of a mask against COVID. Masks have another effect.
Masks protect other people FROM YOU.
If you are wearing a mask, and you are sick, the mask is catching and stopping virtually all your aspiration of the virus. Masks protect others from you. They're not PPE: they're mePE.
This is the effect the scientists are looking for. This is the reason for the government orders.
And the science is showing that almost any mask is highly effective in this role: the non-N95 and homemade masks all work fine.
Some N95 masks actually have a bypass valve so exhalation is not filtered. Those exhalation-valve masks do not work to protect others from the wearer. As a result they are dis-recommended.
This was only discovered in the last couple of months. COVID-19 is, after all, a novel virus - science is learning as it goes along.
You can see where this puts the mask requirement in a whole new light. Previously, one thought, you can decline, and how dare the "nanny state" protect you from yourself, the masks are stupid and don't work... (which is itself a popular trope, see last years's series Chernobyl, where most workers mocked and discarded the sorry PPE).
But now, when we rethink the masks as a "duty to protect others from oneself"... Now, someone refusing to wear a mask is a selfish, narcissistic sociopath.
The employer not only has a right to enforce behavior that protects its other employees... but they have very good non-COVID reasons to want to exclude reckless, other-endangering sociopaths from the company.