Ferguson confirmed the numbers Tuesday in a television interview with CBC's Power and Politics.
Senate sources with knowledge of Ferguson's upcoming report on Senate spending have said that up to 10 senators may be referred to the RCMP for criminal review. Ferguson says that number is "close" but "not exact."
Auditors are challenging the remaining 20 senators on spending worth thousands — as high as $20,000 in at least one case — over travel claims that didn't involve Senate business, as well as questionable office contracts and housing claims.
Those who dispute the auditors' findings will be able to turn to former Supreme Court of Canada justice Ian Binnie, whom the Senate unveiled Tuesday as the special arbitrator who will referee any disputes arising among senators over dubious expense claims flagged by Ferguson.
It's the latest attempt by the Senate to get ahead of what is widely expected to be a critical report on past spending practices.
Ferguson's report is expected to be delivered to the Senate some time next week.
Senators in the most trouble with auditors are expected to avail themselves of the arbitration process, hoping to avoid a hefty repayment order, or having their file sent to the RCMP for review. The remaining senators have already started repaying expense claims challenged by Ferguson's teams, ensuring they won't go to arbitration.
Binnie will be called to intervene in cases where senators who are ordered to pay back disallowed expense claims opt to challenge either the findings of the report or the amount they are required to repay.
Senate Speaker Leo Housakos said current and retired senators in trouble with Ferguson will have the chance for a hearing with Binnie.
"Every single case that the auditor general identifies where there are disagreements will have the arbitration process at their disposal, including those that will be, I assume, referred to the RCMP or any other authority," Housakos told a news conference.
Senators who don't repay the upper chamber will have their salaries clawed back until the Senate recoups all the money owed to it.
Retired senators caught in Ferguson's report will have to sign an agreement that Binnie's decisions are binding, Housakos said. If they fail to repay any money owed, the Senate intends to take those retirees to court.
Housakos said all of Binnie's decisions will be made public.
And Binnie said the new process will be independent, fair and impartial.
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"Every citizen has the right to due process," he said. "The Senate arbitration process ensures this."
The arbitration process wasn't available in the fall of 2013 when the Senate suspended Mike Duffy, Patrick Brazeau and Pamela Wallin without pay over their questioned expenses. All three complained they were being treated unfairly and asked — in vain — for a chance to plead their case before a panel of their peers.
Ferguson said he didn't know the particulars of the arbitration process but, in general, applauded the idea.
"We have talked about the need for there to be some outside independent way of looking at this type of spending so it's not just … senators' spending that's being evaluated by senators," Ferguson said.
"Having some sort of external oversight is important."
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