Canon 1398 says anyone who
procures an abortion incurs automatic (
latae sententiae) excommunication, but it doesn’t say anything about those who
support it. Is there some other relevant canon that I am missing? I looked but couldn’t find any.
I suppose if you consider supporters of abortion to be “an apostate from the faith, a heretic, or a schismatic” they would incur automatic excommunication by virtue of
Canon 1364.
CCC 2089 defines heresy (and
Canon 751 echoes this definition) as “
the obstinate post-baptismal denial of some truth which must be believed with divine and catholic faith, or it is likewise an obstinate doubt concerning the same”. By that definition, those who support abortion could be considered heretics insofar as they deny the Church’s teaching on the morality of abortion.