Rick Ross is facing a new legal challenge ... 'cause a man just sued him, claiming Ross didn't ensure his car show was accessible for disabled people.

A man named Darris Straughter is suing Ross because he says Ross marketed his car show as a dream opportunity to visit his property ... but he says he didn't get the chance ... because a wheelchair-accessible shuttle bus never arrived to get him to the event -- despite claiming he got multiple assurances there would be one.

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Darris says he paid for travel, lodging and bought a ticket -- even selling his car to do so -- to Rick Ross' Car & Bike Show ... and claims he reached out to the venue two weeks in advance to give them notice he needed reasonable accommodation for his wheelchair.

He claims car show organizers told him they'd have a shuttle to take him from the parking lot to the event ... but says, after waiting several hours it never came. He got fed up, gave away his ticket, and went back to his hotel.

Darris and his lawyer, John Hoover Esq., say organizers promised a refund for anyone who didn't get into the event ... but says nobody ever followed up with him.

He's suing Rick for breach of contract, unjust enrichment, and violation of the Americans With Disabilities Act ... and he's asking for damages and an order forcing the car show to provide disabled access in the future.

We've reached out to Ross ... so far, no word back.