The first time Zwingli came in conflict with the Roman Catholic Church was in 1522. This had several causes:

1. The bishop of Constance had protested when churchgoers of Zwingli no longer fasted during the Passion Week. 
2. In a letter to the bishop of Constance, he asked for removal of the promise of celibacy. (He was secretly married with the widow Anna Reinhart.)

Here Zwingli based his view only on the Bible.