Of course. Why wouldn’t it be? Maybe your state has other laws but you are looking out for the welfare of your employees and the public. But I really would not worry as much about the swine flu. Yes, it is serious, but it is hyped way beyond the realities of the situation. I would not require it just for that. Just ask them to stay home for a few more days if you are worried. According to the CDC, “People with H1N1 influenza virus infection should be considered potentially contagious as long as they are symptomatic and possible for up to 7 days following illness onset.”