A cloud remains over the Massachusetts Senate as lawmakers return to Beacon Hill in the new year.

The Senate is scheduled to hold its first formal session on Wednesday since it voted to investigate former Senate President Stan Rosenberg. Investigators from a Boston law firm are looking into whether Rosenberg violated any Senate rules in connection with accusations that his husband, Bryon Hefner, sexually assaulted or harassed several men who had business with the Legislature.

Rosenberg stepped aside as the Democratic leader of the Senate after The Boston Globe reported on the allegations. He remains in the Senate and is working out of a temporary basement office in the Statehouse.

The House also is expected to resume formal sessions on Wednesday after being in recess since before Thanksgiving.