Canonist Ed Peters goes into detail on a current topic with a primer on canon laws related to the consequences of supporting pro-abortion legislation:
Here’s the Shorter Version: First, Canon 916. There are lots of mortal sins out there; if you commit any one of them, you’re not supposed to go to Communion. It’s your obligation to stay away. Next, Canon 915. Some mortal sins are committed under circumstances that, if the Church finds out about them, not only are you supposed to the stay away from Communion, but the Church is supposed to turn you away if you try to receive. Finally, Canon 1331. A few mortal sins are serious crimes under canon law; if you commit one of those, you can suffer the penalty of excommunication, and one of the consequences of excommunication is, you can’t go to Communion.
That seems pretty straight-forward, no? Still, if you want more, read the Longer Version:
Thus the difference between excommunication and exclusion from Communion, a difference seemingly lost on much of the secular media, probably due in part to the fact that the terminology is confusingly similar. Note that he says that for those covered by Canon 915 “the Church is supposed to turn you away if you try to receive.” In this case “the Church” is not just the bishop, but the responsibility falls to the minister of Communion, usually the pastor of the parish.
This was the determination of the Pontifical Council for the Interpretation of Legislative Texts in a declaration issued in 2000:
The discernment of cases in which the faithful who find themselves in the described condition are to be excluded from Eucharistic Communion is the responsibility of the Priest who is responsible for the community. They are to give precise instructions to the deacon or to any extraordinary minister regarding the mode of acting in concrete situations.
Bearing in mind the nature of the above-cited norm (cfr. n. 1), no ecclesiastical authority may dispense the minister of Holy Communion from this obligation in any case, nor may he emanate directives that contradict it.
In other words, no matter what an individual bishop may say about pro-abortion politicians receiving Communion, if the bishop says the individual should refrain from Communion but that it is his individual duty not to present himself, then he is wrong on the second part and right on the first. If an individual is supposed to be refraining from Communion—and the priest knows it, in this case, because the politician is a public figure—then the priest has an obligation that the bishop’s caveats can’t dispense.