Haley's attorney Dina LaPolt tells TMZ ... the bouncers assaulted Haley, without provocation. She also says, "After forcefully removing [Haley] they violently beat her friend, who sustained multiple injuries. We believe that she will be exonerated of all charges once the investigation is completed."

LaPolt added ... Haley plans to take legal action against the bar and the staff.   Former "American Idol" contestant Haley Reinhart got busted for punching a bouncer in the head ... TMZ has learned.

Cops say Haley got arrested early Saturday morning at a suburban Chicago pub called the Lamplighter Inn. Officers showed up around 2 AM after bouncers tossed Haley and some friends for knocking over a table. Cops say as they were being shown the door -- Haley, who stands at a generous 5'2" -- uncorked a closed fist on the bouncer.

She was taken into custody and booked for battery.

Haley went deep into season 10 of 'Idol' ... taking third place. She's currently on the Netflix show "F Is for Family."

Seems like she's vying for a spot in the UFC too.