Willie Nelson has been charged with the unthinkable -- misdemeanor marijuana possession ... TMZ has learned.
Nelson was busted last week after cops found pot on the singer's tour bus at a border patrol checkpoint in Texas.
Cops initially thought Nelson had six ounces of weed -- which could have resulted in a felony charge. But now, officials have determined it was less than four ounces ... so Willie was slapped with a misdemeanor.
If convicted, Willie will be fined -- but not jailed ... but we think Willie can afford it.