Can my employer withhold severance if I refuse to relocate?

My employer is in round one of lay-offs. Severance packets are being offered to everyone as far as I know. I have not been given my severance agreement yet as I believe I am in round two. But I have heard that some people in the first round have been offered positions at a different office over 350 miles away and were told that if they do not accept the position they will not be offered a severance packet. I am concerned as I now have been contacted by the far-away office. I cannot relocate due to personal reasons and am worried that I will be denied severance because of this. Can they do this? Isn't there a limit to how many miles away a transfer can be in order to be considered a reasonable offer?