Can an employer ask for an employees medical information before picking an insurance plan?

Question: My company has asked me to fill out a survey that they will be using to find a different medical insurance plan. The survey contains all of my identification, including social security, as well as several pointed questions about medical history (e.g., AIDS, chest pains, history of cancer, etc). This seemed slightly questionable to me and I was hoping someone could way in with some legal guidelines on what an employer can and cannot do.