Justin Bieber Sued ... You're a Sorry Thief

Justin Bieber is being sued by an indie pop star who claims the Biebs jacked her vocal loop for his monster hit "Sorry."

Casey Dienel, aka White Hinterland, claims the "unique characteristics of the female vocal riff" off her 2014 hit "Ring The Bell" are identical to "Sorry." She also names Skrillex, who produced JB's hit, and its writers as defendants.

Bieber only uses 8 seconds of the riff ... but Casey says he repeats it 6 times in the track. That's not the only similarity ... according to Casey, both songs feature keyboard synthesizers, samples, synth bass, drums, and percussion.

Casey points out her track was a hit in its own right ... racking up more than 800k streams, and Rolling Stone singled it out as a mag fav.

Casey says she warned Bieber to stop using the sample last December but he ignored her.

She wants Bieber to stop playing her tune ... and she wants $$$$$$$$$.