A Conservative senator today bristled at questions auditors have put to her about her expenses, saying she shouldn't be expected to eat airline breakfasts.

"If you want ice-cold camembert with broken crackers, have it!" said Senator Nancy Ruth.

Ruth said auditors had taken issue with "a couple of times that my assistant put in [a claim] for a breakfast when I was on a plane, and they say I should have not claimed because I should have eaten that breakfast. Well, those breakfasts are pretty awful.

"I just don't think they understand anything of what it's like to have to fly around the world to get here to Ottawa."

From the Dec. 1, 2014 to Feb. 28, 2015, Ruth charged $5,799.09 in living expenses in the national capital region and $11,014.87 in travel "between the senator's province/territory of appointment and the National Capital Region."

Ruth lives in Toronto.

NDP take aim at Senate

"Some of these numbers are shocking. We want to know why there were no checks and balances at any point, it seems, when it comes to Senate spending," said the NDP's Charlie Angus. "We're hearing reports of up to $100,000 inappropriate travel spending. That's surprising."

"We'd love to get to work with the provinces and get rid of the Senate," said NDP Leader Tom Mulcair. "It's wasteful and it's useless."

Mulcair on Senate expenses1:17

Senator Marjory LeBreton invited the auditor general to review the Senate's expenses in 2013 when several of its members were caught up in a scandal over claims they made for homes they had described as primary residences.

Former Liberal Mac Harb, who has retired, and Conservative appointees Patrick Brazeau and Mike Duffy have all been charged over their expense claims, while Pamela Wallin faces an ongoing RCMP investigation. Duffy's trial gets underway Tuesday.

On Wednesday, LeBreton walked past reporters trying to speak to her about the auditors' findings. "I have absolutely no comment on anything that is going on with the auditor general or in the court."

40 auditors working full-time

About 40 auditors hired by the auditor general are working on the Senate expenses file in any given month, poring over claims related mostly to travel and housing.

They are looking for evidence that senators may have billed taxpayers for expenses they incurred while not on Senate business. Sources say that could mean expenses claimed for travel undertaken for partisan activities, a trip to a corporate board meeting or personal matters. Auditors are also looking at office spending, contracts, purchasing and international travel.

CBC News has learned 118 current and former senators are being examined. All of them will receive a letter from auditors asking for further clarification on expenses. CBC News has learned 40 letters were sent to senators in the past week, and 78 are yet to come â€” but not all of the letters reveal problems with those senators' expenses.

Some senators said the letters challenge expenses for postage and hospitality expenses, and in each case set out the exact amount being disputed. In some cases, the amounts total thousands of dollars, one senator said.

In those cases, receipts alone are not enough to satisfy auditors. They want proof the expenses claimed truly relate to Senate business.

So if, for example, a senator claims meal and travel expenses for a trip to give a speech at an event, auditors might request a copy of the speech or photos showing the senator at the event. They will then determine whether the speech is really Senate business, or related to some other aspect of the senator's life or work.

None of the senators has yet completed the audit process and been declared clear.

Senators say they've been told the last step in the review will be when every senator receives a final letter from the auditor general, outlining the results of each individual audit. Senators will then be given a chance to comment on the findings.

Those comments will be included in the auditor general's final report.

with files from Hannah Thibedeau, James Cudmore and Chris Hall