Nineteen current and retired senators will be fighting the Auditor-General's findings in front of a binding arbitration process, which will rule on the validity of disputed expense claims worth a total of $542,000.

Among other things, arbitrator Ian Binnie will determine whether taxpayers should have paid for Senator Terry Mercer's trip to the 100th anniversary of a curling club, Senator Elaine McCoy's use of taxis to commute to her office in Ottawa, and retired senator Lowell Murray's trips to his personal residence in Cape Breton.

A retired Supreme Court justice, Mr. Binnie will hear the cases in private, but his findings will be made public once the process is completed. The participants have agreed to pay back the money if he sides with the findings of the Auditor-General.

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Mr. Binnie said he wants written submissions from the 19 senators by August, and will be open to hearing oral arguments. He said the process should be completed in the fall.

"The length of the process will depend on the number and complexity of the responses of the Senators ... to the findings of the Auditor General and, to some extent, on decisions that may be taken by the RCMP ," he said in an e-mail to The Globe.

Auditor-General Michael Ferguson raised questions over the expense claims of 30 senators in a report released last week, eight of whom have fully reimbursed expense claims totalling $75,930. Of the 19 who will be going to arbitration, eight have already offered partial reimbursements to taxpayers, totalling $19,310.

One retired senator, Rod Zimmer, has refused to reimburse taxpayers for any of his disputed expenses, and rejected the offer to take the matter to arbitration. Mr. Zimmer is facing a $176,014 tab related to his residency and travel claims.

Retired senator Don Oliver has reimbursed $23,395 to the government, but refused to pay back $24,692 in other disputed expenses and will not go to arbitration on the remaining amount.

Retired senator Marie Charette-Poulin is in a similar situation, having reimbursed $5,606 in disputed expenses. However, she still faces a bill of $125,828 in relation to expenses that were allegedly for personal use or related to her other job as a lawyer, and has not accepted the offer to go to arbitration.

In total, the three are being asked to reimburse $326,534 by the Senate administration. They could quickly end up in court, as the Senate has said it will sue retired senators who do not submit to binding arbitration.

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All sitting senators have either reimbursed their expenses or gone to arbitration. The Senate administration had threatened to claw back their salaries to recoup the disputed amounts.

In his report, Mr. Ferguson found that Canadians paid a number of senators to go on fishing trips, play golf, attend hockey games, go on holidays, own two homes or get a staffer to bring a personal car back home to Halifax from Ottawa.

The audit cost $23.5-million over two years as the Auditor-General's Office combed through 80,000 expense claims from 116 senators from 2011 to 2013. It identified nearly $1-million in wrongfully claimed expenses.

The eight current and retired senators who have fully reimbursed their expenses are: Government Leader in the Senate Claude Carignan, Leader of the Opposition in the Senate James Cowan, Senate Speaker Leo Housakos, Nicole Eaton, Janis Johnson, Noel Kinsella (retired), Vivienne Poy (retired) and Nancy Greene Raine.

The 19 current and retired senators going to arbitration are: Pierre-Hugues Boisvenu, Sharon Carstairs (retired), Jean-Guy Dagenais, Joseph Day, Colin Kenny, Rose-Marie Losier-Cool (retired), Sandra Lovelace Nicholas, Ms. McCoy, Mr. Mercer, Pana Merchant, Mr. Murray, Dennis Patterson, Robert Peterson (retired), Don Plett, Bill Rompkey (retired), Nick Sibbeston, Gerry St. Germain (retired), Terry Stratton (retired) and David Tkachuk.

The Senate has referred to the RCMP a total of nine cases: Mr. Boisvenu, Ms. Carstairs, Ms. Charette-Poulin, Mr. Kenny, Ms. Losier-Cool, Mr. Oliver, Mr. Rompkey, Mr. St. Germain and Mr. Zimmer.