EXCLUSIVE

Meek Mill was charged with assault Wednesday at St. Louis International Airport after an airport employee on the hunt for a pic triggered a fight ... TMZ has learned.

We're told the airport employee wanted a photo with Meek but the rapper wasn't having it ... and an altercation ensued.

Airport police were called and Meek, along with 2 airport employees, was charged with misdemeanor assault. They were given a summons to appear in court in lieu of arrest.

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Meek is on probation for a weapons and drug conviction, so this could be a violation.

We know this ... 5 minutes before we posted this story, Meek was ordering pizza at the airport just before catching a flight.