OTTAWA -- Ethics Commissioner Mary Dawson is starting an investigation into whether Health Minister Jane Philpott breached conflict of interest rules by contracting a car service linked to one of her campaign volunteers.

Earlier this year, Philpott used Executive Sedan Livery Service for transportation around the Greater Toronto Area, spending $1,709 on March 31, and $1,994 on July 12.

Philpott's office also paid $3,814 for 20 trips to Pearson International Airport. The Canadian Press reported those rates are far above estimates provided by other car services. Reza Shirani, who volunteered an Philpott's election campaign, owns the car service, but it’s unclear whether Philpott knew about the connection.

Philpott apologized for what she called "excessive costs related to travel for my work responsibilities," has promised to repay $3,700 in private car costs, and says her office is reviewing the $3,815 in trips to make sure the cost was fair-market value.

She promised to repay those costs if necessary, based on advice from her departmental officials.

Philpott has also promised to repay $520 she billed for a year of access to Air Canada's executive lounges.

Speaking to reporters in Vancouver Tuesday, Philpott said she's taking full responsibility for the expenses.

"Clearly, we did not have adequate systems in place, mechanisms in my office, to prevent that happening," Philpott said. "But I’ve taken responsibility, I apologized for that and we’ve put steps in place to make sure that doesn’t happen [again]."

Will co-operate with ethics probe

Dawson says she'll probe the use of Shirani's service, the ethics commissioner said in a letter to Conservative MP Colin Carrie, who requested the investigation.

The probe will focus on Section 7 of the Conflict of Interest Act, which says parliamentarians cannot "in the exercise of an official power, duty or function give preferential treatment to any person or organization based on the identity of the person or organization."

Philpott wouldn’t discuss the fact Shirani had volunteered for her, citing the ethics commissioner's investigation.

In a statement Tuesday, Philpott's spokesman said her office received a letter from Dawson and that they will co-operate with the ethics commissioner's probe.

Earlier Tuesday, Prime Minister Justin Trudeau suggested he isn't ruling out possible changes to how cabinet ministers report their expenses.

"We're always willing to discuss and look at new ways of demonstrating the kind of open and transparency across government that we know Canadians expect," Trudeau said following an infrastructure announcement in Barrie, Ont.

"We need to be demonstrating that we are accountable, that we are responsible stewards of the public purse."

Trudeau faced questions over spending by two of his cabinet ministers after CTV News reported Monday that Environment Minister Catherine McKenna is under fire for her spending.

Asked whether ministers should have to post their expenses line-by-line, Trudeau said his government was elected on a commitment to be more open and transparent, "and that's exactly what we're doing."