Immigration agents carrying out a sweeping operation in Minnesota can’t deploy certain crowd-control measures against peaceful protesters or arrest them, a federal judge ruled Friday. The order follows widespread outrage over a fatal shooting, reports of US citizens getting detained and Minnesotans getting asked for documents for no clear reason.

The new restrictions came as word spread that the Department of Justice is investigating Minnesota Gov. Tim Walz and Minneapolis Mayor Jacob Frey over possible obstruction of federal law enforcement, sources familiar with the matter told CNN. The probe raises the possibility of criminal consequences for the two Democrats, who have repeatedly told protesters to remain peaceful and to “not take the bait” that could lead to a heavier federal response.

Despite wind chills that plummeted below zero, throngs of demonstrators protested in the snow Friday night near the Bishop Henry Whipple Federal Building in Minneapolis.