But that group of three senators didn't send the matter to outside auditors until a year later.
Senate sources tell The Canadian Press that Senate finance officials brought their concerns about Wallin's travel to the three-person steering group inside the internal economy committee in late 2011 or early 2012.
Sen. David Tkachuk, the chairman of the committee, then offered to address the issue with Wallin directly, sources say.
When the issue of Wallin's frequent travel to Toronto was raised again in November 2012, Conservative Sen. Carolyn Stewart Olsen and Liberal counterpart George Furey insisted it be sent to an independent audit firm.
When asked about the chronology of events, Stewart Olsen said it's the role of the steering group to forward expense irregularities for review when necessary.
"In Sen. Wallin's case, we made the decision that the whole file should go forward to an external auditor, just to make sure that taxpayers' money was properly looked after," she said.
The report from that audit is expected to come out in late July. It is uncertain whether the Senate committee will be reconvened to deal with its findings.
Wallin has reportedly paid back tens of thousands of dollars in travel expenses already. She resigned from the Conservative caucus late last month.
She has said little about the matter publicly, except that she is waiting for an objective review of her expenses to end before responding to questions.
Tkachuk resigned as committee chairman Tuesday, saying he is about to begin cancer treatment.
He has been criticized for his handling of the expenses review, which has embroiled former Conservatives Wallin, Mike Duffy and Patrick Brazeau, as well as former Liberal Mac Harb.
During the audit into Duffy's expenses, Tkachuk contacted Duffy to ask him about a questionable claim that had been raised by the auditor. Opposition parties accused Tkachuk of tipping Duffy off to what was supposed to be a confidential review.
In addition to raising alarm bells about Wallin, Senate finance administrators had also rejected repeated living allowance claims by Duffy. Those rejected claims did not come out until a thorough review of his expenses was completed and made public at the committee two weeks ago.
Auditor General Michael Ferguson is now in the planning stages for a major audit of Senate expense claims. He told reporters Tuesday that he has free rein to decide the scope of the audit, which could include every single senator or just sample of the upper chamber.
Ferguson will also be able to take a look at how Senate finance administrators do their work, and whether the rules around expenses are working.
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