Strange as it may seem, the answer under current law in the Eighth Circuit and, in fact, in many federal courts across the country, is unclear.
The U.S. Court of Appeals for the Second Circuit has identified the uncertainty and two Second Circuit Judges, Leval and Cabranes, reach opposite conclusions.
Having researched this some years ago, I think Judge Cabranes has it right (Magistrate Judges have no such authority) but Judge Jacobs, concurring, may have it even “righter” when he surveys the lack of agreement on his panel and concludes, “This knot needs to be untied by Congress or by the Supreme Court.”