A federal judge Wednesday threatened to throw out the guilty plea of a veteran U.S. narcotics agent who conspired with a Colombian cartel money launderer — an unexpected twist that could derail one of the most egregious misconduct cases in the history of the U.S. Drug Enforcement Administration.

U.S. District Judge Charlene Edwards Honeywell was expected to sentence the disgraced agent, Jose I. Irizarry, but refused to do so over what she called a “totally unacceptable” legal dispute.