Justin Bieber -- Drugs Seized From Tour Bus Connected with Singer

A bus associated with Justin Bieber's tour was stopped last night at the border between Michigan and Canada ... and authorities seized both marijuana and drug paraphernalia, law enforcement tells TMZ.

Chief Customs and Border Protection Officer Ken Hammond tells us, the bus was stopped at the Ambassador Bridge -- which separates Windsor, Canada and Detroit -- after a drug-sniffing dog detected the presence of weed on board.

Hammond says a subsequent search of the bus revealed marijuana and drug paraphernalia. Justin was NOT on the bus in question.

We're told the drugs and paraphernalia were seized and the driver was issued a citation. The driver and passengers were subsequently released without further incident.

The Ambassador Bridge checkpoint is beginning to develop a reputation for itself -- Rihanna's tour bus was pulled over for the same reason back in March.