Justin Bieber is under the influence ... of a rapper named Lil Twist -- and the rapper may be leading JB down a dangerous path.

Twist was with Bieber in a Newport Beach hotel room last week, where, we're told, the rapper was happily rolling blunts for J.B. and others.

Sources familiar with the situation tell TMZ ... JB and Twist have become tight ... and have been smoking together on a number of other occasions.

You'll recall ... Twist was speeding on the 405 Freeway New Year's Day in Justin's Ferrari when he was pulled over by cops.  A photog was killed trying to snap pics of the traffic stop.  Prior to the accident, Twist and Justin had spent much of the day in a room at the Four Seasons Hotel in Beverly Hills -- where Justin frequently gets a room.

Twist's Twitter profile pic makes it  clear ... he's a fan.

Sources involved in Justin's life who care about him are deeply concerned that Twist has become a powerful negative influence in his life and feel very strongly Justin needs a clean break from the rapper or else bad things are going to happen.


FYI ... Lil Twist is signed by Lil Wayne and close knit with the Cash Money and Young Money crews.