Most mortal sins may be absolved by one’s local parish priest. But usually for pastoral reasons (to make sure that people recognize the seriousness of the offense) there are some reserved cases, such a the sin of abortion that have been reserved. The is was the Catholic Encyclopedia has to say:
However, in some countries, including the U.S., quite awhile ago all priests were given permission to absolve the sin of abortion and to reinstate the person in the Church–and recently in this year of mercy, Pope Francis has extended this permission to all priests.
Fr. Vincent Serpa, O.P.