Boxing champ Julio Cesar Chavez Jr. -- son of the legendary Julio Cesar Chavez -- will have to fight to stay out of jail ... 'cause he was just charged with DUI stemming from an arrest earlier this year.

TMZ has learned ... the L.A. City Attorney has decided to hit Chavez with 3 misdemeanor charges ... 2 for drunk driving and 1 for driving without a valid license.

If convicted on all counts, JCC could face up to a year in county jail and a $1,000 fine.

He's due back in court to face the judge later this month.

Middleweight boxing champ Julio Cesar Chavez Jr. -- son of the legendary Julio Cesar Chavez -- has been arrested for DUI, TMZ has learned.

Law enforcement sources tell TMZ, Julio was pulled over in his black Land Rover for a routine traffic stop last weekend on an L.A. freeway -- and when officers approached the vehicle, they detected a strong odor of alcohol.

The officers administered several field sobriety tests -- and we're told Julio's reflexes weren't quit up to par, so they placed him under arrest.

Julio was subsequently booked for DUI. Calls to Julio's people were not returned.