...but basically it's up to the Bishop:

Benedict's spokesman, the Rev. Federico Lombardi, later said the pope was not setting a new policy and did not intend to formally excommunicate anyone. But Lombardi added that politicians who vote in favor of abortion should refrain from receiving Holy Communion.

Here'sa lengthier one explaining how publicy known you are matterss.

The Catholic Church condemns abortion,3  euthanasia,4  sodomy,5  cloning,6  embryonic stem cell research,7 as well as other attacks against the sanctity of life and the family. It is the obligation of the bishop to follow canon law. Canon Law n.915 mandates the denial of Communion to all "manifest, obstinate, persistent sinners," including but not exclusive to politicians.8

Canon 915 not only protects the Eucharist from sacrilegious reception, but also prevents the faithful from sorrowful scandal.

It's important to understand what 'manifest, obstinate, persistent' means. Many wrongly think it applies only to politicians.9 This is not so.

If a Catholic is a 'manifest' sinner, that means he is 'known,' or 'public.' This must be differentiated from the Catholics who are in the state of 'private' grave sin, to whom their sin is known only to themselves and God. The private grave sinner cannot be denied the Eucharist because their sin is unknown to the bishop, to his priests, and his ministers of the Eucharist.

If a Catholic is gravely 'manifest' and 'obstinate' in his sin, that means he pigheadedly continues to 'persist' or 'stand firm' in grave sin that is 'public' in nature and causes scandal to others. This is quite different from those who persist in 'private' sin.

'Catholic' pro-abortion politicians are certainly manifest, obstinate and persistent sinners and they are thus subject to the provisions of c.915.10

Leaving it up to the Bishop allows for local culture and laws...