If all existing named parties consent to proceed before a magistrate judge, the magistrate judge may rule on a motion to intervene even if the prospective intervenor does not consent to the magistrate judge’s doing so.  28 USC 636(c)(1) requires consent of the “parties” to substantive rulings by a magistrate judge.  A prospective intervenor that has filed a motion for leave to intervene but not yet been granted leave is not a “party” yet and so its consent is not required.

Ninth Circuit Court of Appeals (Murguia, J.); November 18, 2016; 2016 WL 6818863