EXCLUSIVE

Michael Phelps was arrested for driving under the influence in Maryland last night … law enforcement sources tell TMZ Sports. We do not know the details of the arrest — but we're told cops are preparing a statement and are expected to address the media very soon. 

It's Michael's 2nd DUI arrest — he was popped in Maryland in 2004 when he was 19-years-old. He struck a plea deal with prosecutors and plead guilty in exchange for 18 months probation.

We've made multiple calls to Michael's reps — but they would not take our calls. 

Story developing …