According to documents obtained by ET, the Palatine Police arrested Reinhart at Chicago's Lamplighter Inn after she argued with security staff and struck an employee on the head with a closed fist.
She was later released on her own recognizance, and has a court date scheduled for August 2 at 10:30 a.m.
Reinhart’s attorney, Dina LaPolt, said her client denies the allegations in a statement to ET.
"Without provocation, Haley Reinhart was assaulted by bouncers at the Lamplighter Inn," LaPolt said. "After forcefully removing Ms. Reinhart, they violently beat her friend, who sustained multiple injuries. We believe that she will be exonerated of all charges once the investigation is completed. We plan on taking legal action against all those who were involved in this unfortunate incident."
Reinhart, who placed third on season 10 of American Idol in 2011, currently voices the character Bill Murphy on Netflix's F is for Family.