NIF in your case is the same as your NIE.
Numero de identidad Extranjero
People often talk about or ask for your NIE or NIF number. In actuality they are the same. The NIE is used for confirming your identification whereas, if you wish to carry out any fiscal function such as opening a bank account, buy a property, car, boat etc it is referred to as an NIF (fiscal) number. Application requirement and the document issued are the same. (from the Easyjet site).
Easyjet site