Two Mounties are involved, questioning other senators and Senate officials.
They're asking about the audit process into her expenses, about changes that were made to Wallin's calendar entries and about her Senate and corporate schedule.
In August, the Senate's internal economy committee received an independent audit of Wallin's expenses. The audit assessed more than $500,000 worth of Wallin's travel claims and determined that about $100,000 of those were inappropriate or questionable.
In response, the Senate committee imposed restrictions on Wallin's travel and demanded she repay tens of thousands of dollars. And it referred the audit to the RCMP.
The RCMP has not said publicly whether it has opened an investigation.
Earlier this month, Wallin paid back about $140,000 in expense claims plus interest, although she maintains she did nothing wrong.
Also on HuffPost