If the government fails, it would clear the way for over-the-counter sales of the morning-after pill to younger girls.

WSJ: US government files morning-after pill appeal

In 2011, the FDA said it had concluded that the "morning after" pill could be safely used by girls of child-bearing age.

BBC: US judge lifts 'morning after' pill age limit

Obama and Health and Human Services Secretary Kathleen Sebelius have also questioned whether there's enough data available to show the morning-after pill is safe and appropriate for younger girls, even though physicians groups insist that it is.

NPR: Justice Department Appeals Morning-After Case