Senator Pierre-Hugues Boisvenu is no longer in the Conservative caucus after learning he was the subject of an RCMP investigation in the wake of the auditor general's exhaustive two-year spending review.

Boisvenu, who was Prime Minister Stephen Harper's point person on law and order issues in Quebec, is one of nine former or current senators whose cases will be recommended by the auditor general to the RCMP for criminal investigation.

‎Sources tell CBC News that Liberal-appointed Senator Colin Kenny is also among the nine.

The other seven have all left the Senate. They are: Liberal-appointed Sharon Carstairs (Man.), Marie-Paule Charette-Poulin (Ont.), Rose-Marie Losier-Cool (N.B.), William Rompkey (N.L.) and Rod Zimmer (Man.) and Conservatives Donald Oliver (N.S.) and Gerry St. Germain (B.C.).​

Boisvenu announced his "voluntary" removal from the Conservative caucus in a statement late Thursday, adding he will explain his decision in more detail in the coming days.

Senate Speaker Leo Housakos tells CBC's Rosemary Barton the auditor general's report delivered to the Senate Thursday will strengthen transparency in the Senate. 11:07

Last year, Boisvenu was cleared of wrongdoing by the Senate ethics officer after attention was drawn to living expense claims filed when he was found to be dating his political assistant.

Zimmer made headlines as a sitting senator in 2012 over a disturbance on an airplane with his wife.

Sitting Senator Colin Kenny is among nine current and former senators facing RCMP investigation over their expenses. (Tom Hanson/Canadian Press)

Another 21 senators, including the three most powerful figures in the Senate, will be flagged to repay inappropriate expenses. Those include Senate Speaker Leo Housak﻿os, government leader Claude Carignan and Opposition leader James Cowan.

Housakos and Cowan have vowed to take the auditor general's conclusions to an arbitrator appointed by Housakos to settle disputes over the auditor general's findings. Carignan said one of his staff members has repaid about $3,000 in expenses.

Housakos told CBC News he would act on the auditor general's recommendations.

"If there's recommendations in that report to refer specific cases to the RCMP — I've said it before, I'll say it again, and absolutely, we will do it," he said. "There is no room in this institution for deliberate impropriety. None. I won't accept it, my colleagues won't accept it, the people of Canada won't accept it."

The At Issue panel discusses the latest in the Senate expense story and the Truth and Reconciliation Commission. 14:25

Report public Tuesday

The auditor general's report will not be made public until next Tuesday, but copies of the report were handed over to the Senate Thursday.

The Prime Minister's Office says it didn't receive a copy of the report on Thursday. But numerous sources tell CBC News that the PMO will be involved in drafting the response of Conservative senators.

It's been nearly two years since the auditor general was called in to review spending by senators, including travel and living expenses. The review included 116 current and former senators over several years.

The spending habits of suspended senators Mike Duffy, Patrick Brazeau and Pamela Wallin, as well as retired senator Mac Harb have already been investigated by the RCMP.

Duffy has pleaded not guilty to 31 charges of fraud, breach of trust and bribery in a continuing trial in Ottawa. Trials for Brazeau and Harb have not begun, while Wallin has not been charged.