The the article I just linked. It says even the Catholic Church isn't sure.
Well, your article is wrong:
The Catholic Church opposes Plan B not just because it's birth control, but because it considers use of Plan B to be, in Cardinal Egan of New York's words, "a chemical abortion."
And from the United States Conference of Catholic Bishops:
(Take Note how they call it an abortifactant)
Comments on Proposed FDA Regulations on the Distribution of Emergency Contraceptives