British North America Act, 1867, S. 31
31. The Place of a Senator shall become vacant in any of the following Cases:
1. If for Two consecutive Sessions of the Parliament he fails to give his Attendance in the Senate:
2. If he takes an Oath or makes a Declaration or Acknowledgment of Allegiance, Obedience, or Adherence to a Foreign Power, or does an Act whereby he becomes a Subject or Citizen, or entitled to the Rights or Privileges of a Subject or Citizen, of a Foreign Power:
3. If he is adjudged Bankrupt or Insolvent, or applies for the Benefit of any Law relating to Insolvent Debtors, or becomes a public Defaulter:
4. If he is attainted of Treason or convicted of Felony or of any infamous Crime:
5. If he ceases to be qualified in respect of Property or of Residence; provided, that a Senator shall not be deemed to have ceased to be qualified in respect of Residence by reason only of his residing at the Seat of the Government of Canada while holding an Office under that Government requiring his Presence there.