Justin Bieber Sued: It's Too Late to Say Sorry ... You Owe Us $650k!

Zut alors! Justin Bieber just got sued in Montreal by a promotional company that says he destroyed its biz with one little tweet.

The promoter, Team Productions, says they had a deal for Justin to do an appearance at Beach Club last August. JB was supposed to do a couple songs and then hang out with fans -- but the event was scrapped.

Team Productions says it paid Bieber $250k when he signed the deal, and promised another $175k right before the event. But TP says it noticed Justin wasn't pumping up the gig on his social media ... as the contract required him to do.

The promoter says Justin demanded they pay the rest of the money or he wouldn't show -- but since Justin wasn't plugging, Team Productions wanted a discount. Negotiations started, but failed ... leading Justin to tweet on the morning of the event he would be bagging out because the promoter lied.

Our Bieber sources claim TP didn't have the $175k balance when it came time to pay -- even though it had been using Justin's name to promote. TP insists it had the cash, but just wanted the cut rate.

Team Productions says it's been branded a liar and as a result no one wants to work with them. They want at least $650k in damages.