oral generic levsin

I would like to know why the oral generic levsin cannot be chewed. I had taken it one other time and was not informed it should'nt be chewed, so I chewed those and didnt seem to have a problem. This time when I got it filled there was a sticker on the bottle that stated not to chew or crush it. Would like to be informed about this. Thank you for your time.

Sincerely,  Tammy