A U.S. senator, likely Maryland Democrat Benjamin Cardin, is using an anonymous hold to stifle debate on a bill giving D.C. Mayor Adrian Fenty control of the city’s public schools.

The mystery senator used the chamber’s prerogative to place a hold on the measure immediately after it passed the House on Tuesday, a mere week after its introduction by D.C. Del. Eleanor Holmes Norton. Fenty’s school takeover, and subsequent demotion of the D.C. Board of Education, includes an amendment to the District’s Home Rule Charter and therefore requires congressional sanction.