Backstreet Boy Sorta Threatens AJ and Nick

2/8/2009 3:23 PM PST BY TMZ STAFF
Brian Littrell has seen two Backstreet Boys fall off the wagon recently -- AJ McLean and Nick Carter -- and the guy was serious when he told us they better "clean their act up" if they want to remain Backstreet Boys.

Thing is, Brian said he and the boys are hitting the studio tomorrow to start a new record... so he -- and his trusty new cast -- can knock some sense into 'em.