Do I have to explain what I do with my days off?

My salon ran a charity food drive on a recent Sunday. I work Tuesday through Saturday and am unavailable on Sundays. I have kids and my husband works Sundays, hence my non availability. The owners were FURIOUS that more staff didn't sign up to volunteer their time. THey made it clear that they were more concerned with bad PR than feeding the poor. They demanded that the management provide an itemized list of each person who didn't sign up and EXACTLY what they were doing that day that prevented them from volunteering. THere will be repercussions to those of us that didn't sign up, I can promise that. Is my employer within it's legal rights to ask this of the management? Am I obligated to provide the details of my Sundays off?