Canon Law already punishes Catholics involved in abortion with automatic (latæ sententiæ) excommunication:
Can. 1398 A person who procures a completed abortion incurs a latæ sententiæ excommunication.
This includes all Catholics involved: the woman, her family, the abortionist, assisting nurses and doctors, and even those on medical ethics boards who approve of the direct killing of the unborn (cf. the 2010 case of the excommunication of Sr. Margaret McBride).
cf. canonist Dom Augustine's commentary on those who perform abortion.
The question the Polish bishops are dealing with is whether those involved in abortion should be penalized by civil authorities. When Church and State were not so separated as today, Catholics guilty of a crime could choose whether to be tried in an ecclesiastical court or a civil court. Perhaps the Polish bishops believe Catholic women who procure abortions do not need to be tried twice when the Church has already judged and punished them with excommunication. Non-Catholics cannot be tried in ecclesiastical courts because the Church only has jurisdiction over Catholics. Thus the question becomes: Can Church authorities tell civil authorities how to punish non-Catholics involved in abortion?
This is related to the question St. Thomas Aquinas addresses in the Treatise on Law of his Summa Theologica I-II q. 96 a. 2: "Does it belong to the human law to repress [as with punishment or coercion] all vices [e.g., abortion]?." He answers (c.):
[H]uman law is framed for a number of human beings, the majority of whom are not perfect in virtue. Wherefore human laws do not forbid all vices, from which the virtuous abstain, but only the more grievous vices, from which it is possible for the majority to abstain; and chiefly those that are to the hurt of others, without the prohibition of which human society could not be maintained: thus human law prohibits murder [e.g., abortion], theft and such like.
Thus, human law should repress abortion. Exactly how it should be repressed inside the civil sphere is outside the jurisdiction of leaders of the Church and must be left to the prudence of civil authorities (cf. St. Thomas's Summa II-II q. 67 a. 1 question "Can a man justly judge one who is not subject to his jurisdiction?").