If a law is passed it should probably follow the same lines as Conscientious Objector legislation.
During Vietnam, many people objected to the war on "moral" grounds (as many, probably, as are objecting to the Iraq war today.)
But there were two qualifications for conscientious objectors: 1) they had to be opposed to ALL wars and 2) they had to be a member of an organized religion that opposed war--Quakers, for example. (If not, they had to have tons and tons of substantiating evidence.)
And so a nurse or doctor objecting on moral grounds should 1) oppose ALL abortions, not just abortions after the first trimester. They should oppose abortions no matter how compelling or how frivolous the reason is. 2) They should belong to a religious group that opposes abortion. Why?
Because there is no Constitutional guideline for when life begins--there are only religious guidelines. A better definition might be when "ensoulment" begins.
I think this would be fairer and would take away the air of pompous self-righteousness that can so often accompany requests like these.
The requester is basically saying: "I belong to a religious organization that says that life (ensoulment) begins at conception. I respect the beliefs of my colleagues to act otherwise, if their religions or belief systems are different from mine, because there is no legal definition in this country of when life begins."
Sure, it's a tough standard. And I daresay that most medical personnel are probably reluctant to assist in 22 week abortions
And a high burden of proof will insure that what is basically a religious conscientious objection doesn't become a loophole to get out of parts of a job an employee doesn't like.