[chris_bdba]

The morning after pill makes the woman shed the lining in her uterus because of the massive dose of hormones. If there is an embryo that is beginng to attach it would cause it to be shed too.

[flintsilver7]

From Wikipedia:

The United States FDA states that progestin-only ECPs like Plan B work by preventing ovulation. It also says "it is possible" that progestin-only ECPs may interfere with the blastocyst implanting in the uterine lining, and that they have no effect on pregnancies if taken after implantation.[108][109]

Hormonal progestin-only and combined estrogen-progestin emergency contraceptives such as Yuzpe regimen or Plan B differ from the anti-hormonal drug mifepristone (also known as Mifeprex and RU-486). Yuzpe and progestin-only emergency contraception will have no effect if taken after implantation, whereas mifepristone can induce abortion if taken after implantation.

You are confusing high-dose hormonal contraception with actual abortifacients.