For years, anti-abortion activists have objected to the use of emergency contraception, arguing that it essentially causes an abortion by preventing an already fertilized egg from implanting in the uterus and thereby terminating a pregnancy.

They didn't get that idea out of nowhere. Inside of every package of emergency contraception, the so-called morning-after pill, is a U.S. Food and Drug Administration-approved warning that says the drugs -- used to prevent pregnancy after unprotected sex -- may work by blocking fertilized eggs from implanting. 

But, according to an exhaustive report released by The New York Times this week, there is one big problem with that explanation - the science doesn't support it.

An analysis of more than a decade's worth of research on the issue since the market release of Plan B in 1999 showed that studies have not established that emergency contraceptive pills prevent fertilized eggs from implanting. Scientists reportedly considered that possibility before they had a clear understanding of how the pills worked.

Instead, most studies have concluded that the pills delay ovulation, or the release of eggs that occurs before they are fertilized, until sperm is no longer potent. The explanation has become so widely accepted among the scientific community that it is backed by the World Health Organization and the International Federation of Gynecology & Obstetrics, which say the three emergency contraception drugs currently on the market do not inhibit implantation.

Based on the belief that a fertilized egg is a person, conservative politicians and religious groups have railed against emergency contraception, demonizing it as akin to abortion in an election cycle where both abortion and contraception have become hot-button issues. 

Republican presidential candidate Mitt Romney recently called emergency contraceptives abortive pills. Similar statements came from his rivals Rick Santorum and Newt Gingrich during their campaigns.

The conservative personhood movement, which has campaigned for ballot iniatiatives in several states that would legally define fertilized eggs as human beings, has gone as far as opposing both emergency contraception and hormonal birth control pills because of their purported abortion-causing effects.

The FDA is apparently aware that the science supporting those emergency contraception labels is either wrong or outdated. FDA spokeswoman Eric Jefferson told the New York Times that the emerging data on Plan B suggest that it does not inhibit implantation, but he refused to discuss when the agency might consider revising the warning labels.

Plan B was the first emergency contraception pill released on the market, and is still the most widely used. There is reportedly less science available on the effects of the other brands, Ella and Next Choice.

How the implantation warning got on the labels is still a bit of a mystery.  According to the Times, a review of hundreds of pages of approval documents regarding Plan B did not include any discussion of evidence supporting the supposed implantation effects.  Jefferson would not comment on why the FDA still included that side effect on the Plan B warning label, despite the drugmaker's complaints.