Alien invasions seem to be a great way to bring out the best and worst in our social/political situation. The classic John Campbell style heroism had its best modern representation to me in Independence Day. But just as often it's more dystopian, with subjugation bringing out (or based on) our weaknesses. Sometimes it's to save us, as in Octavia Butler's Xenogenesis series. There might be something of that going on in They Shall Salt...and in this case the social weakness is the abortion issue.
The narrator is a farmer/survivor of the invasion. Humans are basically scraping by and a sad bunch. Aliens come along and mine the area with glass bead bombs (thus we have a commentary on modern warfare as well), along with other social engineering. They offer to take in pregnant mothers and assist them through birth, but what happens next might be sinister. So the story revolves around what happens when the narrator's sister becomes pregnant.
Johnson makes things interesting by throwing in an almost-sympathetic alien that discusses their efforts to rebuild human society in foreign NGO/UN speak. Would be funny if it wasn't so sad.
Read this for a tweak at your conscience. It's one of the things speculative fiction is good for. Three stars from me.