Historically it was legal; I want to say it was banned a couple years back, but I'm not confident about that.
http://www.forbes.com/sites/halahtouryalai/2013/06/11/yes-ba...
In 2012, banks took in $32 billion in overdraft fees up $400 million from the previous year. The record was hit in 2009 with $37 billion in overdraft fees collected by banks.