A quick Google search of St Nicholas + Arius throws up quite a few sites. Here's one to start you:
"As he was present for the First Ecumenical Council in AD 325, we definitely know he was born at the end of the third century. That Council was called to condemn the heresy of the Alexandrian monk, Arius, who denied the Divinity of Christ. This was the Council where the term "Orthodox" was first generally used to define the true faith about and in Christ, as opposed to the heretical musings of Arius and others ever since.
Nicholas was shaken to the core of his being at the very thought of Arius' impiety. He was consumed by a holy zeal and, in righteous anger, struck Arius across the face during the Council meetings. His fellow Orthodox Christian Bishops thought this action was unbecoming, and therefore immediately censured Nicholas by taking from him the symbols of his episcopal office, his Pallium ("naplechnyk") and his Gospel. As they did this, an apparition took place. Christ and the Virgin Mary-Theotokos appeared on either side of Nicholas, Christ holding the Gospel-book and the Mother of Christ our God holding the Pallium. At that, the Council reinstated Nicholas. This miracle is celebrated on his feast, December 19, according to the Old Calendar, to this day. This depiction of St. Nicholas has been the most popular in his iconography ever since". http://www.stnicholascenter.org/
I'm not qualified to pontificate about the authenticity of either St Nicholas's presence at the Council or his assault on Arius, but I derive great inspiration from a Bishop prepared to stand up for truth. Bishop Spong watch out!