communication rights

I have noticed that my cell phone will not get any signal for sending or receiving calls while in two certain casinos. However, it works fine in their hotel or anywhere else outside the casinos. I heard that they block the signal. Is this true? This doesn't seem right. They should at least be required to post a disclaimer to the patrons. Doesn't seem like it should be legal to block a person's right to communicate with a cell phone. What about possible emergency calls?