OntarioSheltie
Forums Celebrity
I found this, which was posted by the Canadian Gov't about the active ingredient in the preventic collar (Amitraz). It looks as though they're requesting label clarification, but I don't see anything about it becoming illegal or it being pulled from the shelves.
http://www.hc-sc.gc.ca/cps-spc/pubs/pest/_decisions/rev2011-04/index-eng.php
http://www.hc-sc.gc.ca/cps-spc/pubs/pest/_decisions/rev2011-04/index-eng.php