Justin Bieber -- Loud Partying Could Trigger Probation Violation

Justin Bieber is playing with fire after cops responded to complaints at his Beverly Hills condo 6 TIMES over the weekend ... and his freedom is literally on the line.

Cops received 4 separate complaints for loud music and partying on the roof top Saturday night and they sent patrol cars each time -- at 8:30 PM, 12:50 AM, 1:50 AM and 3:00 AM. We're told Bieber was not cited because he agreed to turn the music down.

There were 2 other incidents involving disturbances with fans and paparazzi.

Here's what's so significant ... Bieber is currently on 2 years probation for egging his neighbor's house. Law enforcement sources tell TMZ ... if the Bev Hills PD cites Bieber ... they will forward the matter to the L.A. County Probation Dept., which could trigger a probation violation and then he's in jail territory.