Mortal sin is mortal sin. Denial of communion requires persistant, manifest expression of grave sin.
1. Dissent from Church teachings.
2. Persistant - ie, the dissent has to be over a certain period of time.
3. Public - ie, the dissent has to be expressed where other people can hear.
4. Grave. It has to be over a matter that would be considered mortal sin. Public endorsement of abortion qualifies.
5. Other interventions have to have failed.
Denial of communion isn't the first step - but if other measures have been tried and haven't worked, then yes, denial of communion is appropriate.
And Phil - all the politicians who claim to be pro-abortion and 'Catholics in good standing' should be denied communion. ESPECIALLY Pelosi. Her dissent goes beyond 'being an irritating nuisance', to 'actively misleading others as to what the Church actually teaches.'