Scottie Pippen and his wife are FURIOUS at Christian Laettner -- claiming he still hasn't paid them back the hundreds of thousands of dollars he owes them ... and they want to collect, NOW.

Around 2007, Pippen invested a ton of money with Laettner and his partners to buy a stake in the Memphis Grizzlies ... but when the deal fizzled, he never got his money back.

Pippen sued Laettner and his partners and was awarded a $2.5 million judgment -- but has NOT received the full amount.

Enter Larsa Pippen ... who took the beef public this week -- tweeting at Laettner, "Hey @laettnerbball are you ever gonna pay us back homie?"

"It's crazy you've been f***ing us around forever @laettnerbball. Homie how do u sleep at night."

Sources connected to the case tell us Laettner still owes at least $600,000 to the Pippens.

Yeah, we'd be pissed too.