If you are in the Republic of Ireland and the job was too, and you believe you have a genuine case due to religious discrimination, you can sue under the Equality Act 2004, which specifically deals with discrimination under the following grounds:gender, marital status, family status, age, race, religion, disability, sexual orientation and membership of the Traveller community.
Contact the Equality Authority, or see
http://www.equality.ie/
A summary of the basis of the act:
http://www.equality.ie/index.asp?locID=17&docI D=-1