I think the key here is whether or not the provide accommodation for other employees with temporary work restrictions. If they do, I don’t see how they avoid providing similar accommodations to pregnant women. On the other hand, if they do not provide accommodations for other employees with temporary limitations, then they should not be forced to provide them for pregnant women.
That is not saying they should not have a way to provide temporary light duty for employees where possible - it is a way to keep good employees who may be injured or otherwise incapable of working at full capacity for a short time. But they should not be forced to do so.
I find it hard to believe in the life of UPS they’ve never had a pregnant driver before.
I wonder how they handled it before now?