New York exemptions can be tricky because school officials may challenge the sincerity of your request for a recommendation. If your reasons for seeking the exemption are bona fide religious, then you should not have a problem. Just write a request for an exemption explaining why your religious beliefs forbid immunization.
If you have health concerns about vaccines, make sure you talk to your doctor before getting the exemption because you are leaving your child open to contracting potentially dangerous diseases by not vaccinating.
I would try to get help from a not-for-profit organization like the National Vaccine Information Center first. If you aren't satisfied, then go to the attorney because an attorney can be expensive and unnecessary. An attorney charged a relative of mine $500 for a letter that she could have written herself. I found this to be unscrupulous because the relative lived in New Jersey were an exemption-seeker never has to prove the sincerity of her religious beliefs - she just has to write a letter stating that her religious beliefs contradict vaccination.