Your supervisor has the legal right to discuss your religious beliefs with you or other employees if he or she wishes to do so. This may include an invitation to participate in church services. However, your supervisor cannot persist to the point of being hostile, intimidating, or offensive. Also, your supervisor cannot make any aspect of your employment, such as pay raises, promotions, or job assignments conditional on you attending his or her church.
If the employer does not make your supervisor stop in this situation, you could claim that you have been subjected to a hostile work environment on the basis of religion, and may have the right to initiate legal action against your employer. If a term or condition of your employment, such as a pay raise or promotion is affected by religion, your employer may be liable for the supervisor's action.
When confronted by a supervisor who wants to discuss religious matters or for you to participate in church services, the first step is to let that person know that the discussion is making you uncomfortable and that you do not want to talk further about religion nor attend church services. That may resolve the problem, as your supervisor might not have previously realized your objections or discomfort with the subject. If, however, the problem persists or your employment starts to be affected, you may need to notify another supervisor or your company's human resources department. You could also consult with a lawyer about filing a religious discrimination claim.
Your company should have a policy for dealing with harassment and discrimination complaints, including complaints of religious harassment and discrimination. Once your employer is aware of the problem, it must take steps to address it.