Taking communion when not baptized?

I was at a wedding ceremony yesterday where they invited all "baptized Christians" to take communion. This kind of confused me. I thought that communion was symbolic of the last supper where he gave the bread and wine to his dinner companions. Those men and women were certainly not baptized. So, what does it matter to the church if you take communion if you are not baptized? Even if it is "against" their rules, does it really matter to God?