Plan B does not prevet fertilization it causes a spontanous abortion by making the uterus hostile to the fetus.
plan b works by preventing a pregnancy--it won't work if you are already pregnant. it is not RU-486, which terminates a pregnacy.
i'm all for working to outlaw abortions--and for restricting the sale/use of RU-486, but i don't see why it's necessary to restrict the ability of adults to acquire and use contraception.