This appears to be true. According to the Chicago Sun Times, Edward York, a staffer of Illinois Democratic Senator Tammy Duckworth, was fired after he was "accused of misrepresenting himself as an attorney and falsifying an official form to visit and secure the release of a Staunton restaurant owner detained by immigration agents." Similar reporting comes out of St. Louis Public Radio, an NPR affiliate. Their reporting notes that "ICE detained Ismael Ayuzo Sandoval last month for violating four prior deportations and having been convicted in a 2008 DUI case. His detention prompted a rally in the small community of Staunton."
ABC7 Chicago reports that, in a letter to Todd Lyons, Immigration and Customs Enforcement Acting Director, Duckworth states that "upon reviewing the matter, I can confirm that neither I, nor my leadership team, was aware of, authorized or directed what your letter describes as the employee's conduct".