Ethics commissioner Mary Dawson is now examining whether Health Minister Jane Philpott violated the Conflict of Interest Act in her use of a high-end car service owned by a Liberal supporter.
Dawson's probe, to be conducted in private, will focus on a section of the act pertaining to "preferential treatment."
It comes after Conservative health critic Colin Carrie wrote to the commissioner over the revelation that Philpott paid a limousine company $1,700 on one day for service and more than $1,900 on another day.
The commissioner cannot comment on the review, but a public report will be issued once it is complete.
Philpott announced last Thursday she would repay the cost of these trips totalling just over $3,700, while admitting these were "excessive costs" related to her work travel.
The minister's department is also examining 20 rides from her home to Toronto's Pearson International Airport totalling $3,815, while it also conducts a wide-ranging review of all other ministerial expenses.
She has promised to pay back any other filings deemed to be inappropriate.
"We will make sure that we do an appropriate review that involves working with the department, that involves working with my office, whoever needs to be involved in that to make sure it is done properly," Philpott said Tuesday in Vancouver.
Reza Shirani — the owner of the vehicle company who canvassed for the minister during the last federal election — told The Canadian Press the minister was driven in a Lexus ES 300 and admitted he was personally in the driver's seat on July 12.
On that day, Philpott billed taxpayers a total of $1,994 for transportation around a speaking engagement at the Assembly of First Nations annual meeting in Niagara Falls, Ont.
Philpott's office said Tuesday it has received notice from the commissioner.
"The minister will work in full co-operation with the conflict of interest and ethics commissioner," it said in a statement.
Carrie said he trusts the commissioner will give Philpott's use of the company a "thorough review."
"The minister knew this was a partisan, a supporter of hers," Carrie said in an interview. "She utilized the service to the point which is up to three times the going rate. ... Canadians are outraged."
The fact the ethics commissioner is looking into this issue shows the matter is serious in nature, NDP MP Charlie Angus said Tuesday.
"The issue of getting caught and paying the money back is secondary to the larger issue that ministers of the Crown are obliged to follow very clear rules on ethics to make sure that they're not being seen to be giving preferential treatment to friends and insiders," Angus said.
"If that happened in this case, then that's a breach of the minister's own code and a breach of the ethical guidelines. It has to be investigated."
The minister is also reimbursing taxpayers for $520 for the use of Air Canada lounges in North America and Europe.
Late Monday, the minister promised to repay the money after the Opposition Conservatives used the Access to Information Act to obtain the receipt for the one-year "Maple Leaf Club North America Plus" membership. A copy of the document was provided to The Canadian Press.
Environment Minister Catherine McKenna has also been under the microscope for her spending after it was revealed she spent $6,600 for photography documenting the COP21 climate change conference in Paris.
"This is a long-standing practice under previous governments, including the Conservative government, because clearly pictures are an important way that we communicate the government business to Canadians," McKenna said at an Ottawa event.
There are ways to reduce costs, she added, noting her department will conduct its own review of expenses.
The government originally thought the Paris photography cost was higher, but McKenna acknowledged her office made a erroneous currency conversion.
The minister still owes Canadians an apology and a repayment, said Quebec Conservative MP Gerard Deltell.
Prime Minister Justin Trudeau said Tuesday the Liberal party "led the way" on proactively disclosing expenses in 2013, adding his government will continue to look for "new and more robust ways" of disclosing the use of public dollars.
"We are always willing to discuss and look at new ways of demonstrating the kind of openness and transparency across government that we know Canadians expect," Trudeau said in Barrie, Ont.
The prime minister has offered all talk and no action so far, Carrie said.
"There's nothing there that will say that the prime minister will actually do something about this," he said. "It is a trend — we've seen it with the minister of health, now the minister of the environment, and he should be taking a proactive approach to examine his other ministers."