Tour Bus Companies -- We're WARNING Drivers About Notorious TX Checkpoint

Several large tour bus companies tell TMZ, they are WELL AWARE of the perilous border checkpoint In Sierra Blanca, Texas -- where multitudes of celebs have been arrested for sneaking drugs on board their buses -- and now, they're taking steps to avoid the same fate.

You'll recall, rapper Nelly's tour bus was pulled over at the notorious checkpoint Wednesday night -- and police claim they found heroin and mass amounts of marijuana on board. A passenger on the bus (not Nelly) fessed up to owning the drugs, and was placed under arrest.

But the Nelly incident was only the latest in a long string of celebrity drug busts at Sierra Blanca -- the list also includes Fiona Apple, Willie Nelson, Snoop Dogg ... it goes on and on.

Now, several bus companies tell TMZ, they're aware of the potential risks associated with driving through Sierra Blanca, so they're warning their drivers to stay alert and keep an eye out for any contraband on board their buses.

One company says their drivers now inform passengers about the checkpoint ahead of time, giving them "a warning to abandon all illicit items if they do happen to sneak some aboard."

Meanwhile, another says, “It’s just idiotic. Just plain idiotic to risk having something like that on board. You’d have to be stupid to allow that kind of stuff on the bus. That’s why we make sure that doesn’t happen on our line.”