If the mother is allowed to abort against the father's wishes, then this would only be fair.
The father would give up any rights he has to the child, completely disowning him in the process. He does not get to be on the birth certificate and is legally not the father.
The mother should be allowed to do this as well, with the added stipulation that the father who does want to maintain custody is held liable for the medical bills incurred by the mother as a result of the pregnancy.
In general though, I'd be against all of this. Abortion bad. Deadbeat parents bad.
Raise your kids. Don't kill or disown them