The Justice Department 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.

A person familiar with the matter told CNN that a grand jury has issued subpoenas for both men as part of the investigation. But Walz’s office had not received any notice as of Friday evening, according to another source familiar with the matter. It was not immediately clear when Frey and Walz would receive the subpoenas.