A panel of lawmakers led by Reps. Charlie Dent (R-Pa.) and Yvette Clarke (D-N.Y.) will determine whether Radel violated the House Code of Conduct or broke any other laws or regulations related to his responsibilities as a lawmaker.
The launch of a formal probe may compel the panel to ask Radel about his history of substance abuse and ultimately could result in a formal reprimand by the full House.
Radel, 37, pleaded guilty on Nov. 20 to a misdemeanor drug-possession charge in D.C. Superior Court. He was sentenced to one year of probation, is undergoing substance abuse treatment in Florida and has said he will remain in office.
Although House Republican leaders haven't called for his resignation, Florida GOP officials have called on Radel to step down, saying his continuing in office would serve as a distraction.