We are a non-union company and we use space at a building that does not belong to us because we are Vendors'. Recenlty we have been asked to move to due this company needed space. The move is scheduled and taking place on 8/1/08. We have been asked to come in on Saturday 8/2/08 to unpack our things. I am being told by HR that our VP can do what ever he wants if he makes this mandatory. But we are not working-only unpacking. I have a third of my staff traveling 50+ miles to unpack that will take an hour. So they are looking at 3 hours of thier time that they will not be paid for just to unpack. Can they do this? If so, do they have to pay employees for at least 4 hours in Ohio?

yes, they can do this. But no, Ohio has no law requiring a mandatory four hour shift, or any other kind of minimum shift or reporting pay rule. Non-exempt employees would be due pay for the number of hours they "worked" (unpacked); exempt employees would be due no additional compensation over and above their regular salaries.

Can you tell me if this is also applies to temporary employees?

It applies to all employees, regardless of their status.