Final answer:
The ethical principle challenged when a nurse refuses to assist with an abortion procedure is autonomy.
Step-by-step explanation:
The ethical principle that is challenged when a nurse feels bound to refuse to assist with an abortion procedure is the principle of autonomy. Autonomy is the right of individuals to make their own decisions about their bodies and healthcare, without interference or coercion from others. In the context of abortion, a nurse may feel conflicted if their personal beliefs or values conflict with the patient's decision to have an abortion. This ethical dilemma highlights the importance of respecting patient autonomy while also balancing the nurse's own ethical beliefs and professional responsibilities.