Klein was arrested and convicted of DUI back in 2004 -- and because of that prior arrest, California law requires that he serve a minimum 4 days in jail if he's convicted of DUI again.
But that's not all -- there's a new law going into effect in July -- which would apply to Klein if he's found guilty after that date -- that requires multiple DUI offenders to have an "ignition interlock system" installed in their vehicle if they wish to drive.
The system is essentially a breathalyzer test that's synced up to the car -- and if he ain't sober, the car won't start.
TMZ has also learned Klein wasn't alone when he was popped early this morning -- there was a dog in his car that a friend retrieved after he was busted.