http://216.239.39.104/search?q=cache:6AzNZXxQC_IJ:www.hutchinsoncreditunion.com/news/hutch_in_touch/Oct2000news.pdf+%22Credit+union%22+OR+%22credit+unions%22+%22Monthly+transaction+limit%22&hl=en&ie=UTF-8
It's called Regulation D.
I used to work in mortgage banking, so this is definitely not my area...