Opposition parties are calling on Justin Trudeau to pay back taxpayers for his pricey trip to the Aga Khan's private island after the Ethics Commissioner ruled the Prime Minister broke Canada's ethics law over two all-expenses-paid family trips to the Bahamas.

Conservative ethics critic Peter Kent said Mr. Trudeau owes Canadians some, if not all, of the $215,000 tab for his holiday in December, 2016, which is the reported public cost associated with his family vacation to Bells Cay.

"The Prime Minister should consider making good on a significant part or perhaps all of the $215,000 in security costs, in staffing costs, in technical costs, in Prime Minister's Office support costs – financed with hard-earned Canadian taxpayer dollars," Mr. Kent said in an interview.

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In a report released on Wednesday, Ethics Commissioner Mary Dawson found that the Prime Minister violated four sections of the Conflict of Interest Act regarding the two family trips last year to Bells Cay. The private island is owned by the Aga Khan, the billionaire spiritual leader of the world's Ismaili Muslims, whose organizations deal frequently with the federal government.

Mr. Kent said repayment would show the Prime Minister takes the Ethics Commissioner's ruling seriously. The findings did not come with any sanctions other than a public scolding.

"In the United States, there would be calls for impeachment," Mr. Kent said. "Heads should roll … I can't believe that there isn't an adult in the Prime Minister's Office who didn't recognize immediately the problems here."

NDP MP Nathan Cullen added that Canada's ethics rules need to come with a concrete sanction if they are to be effective.

"What's the point of having a law to stop bad behaviour if the penalty is wagging your finger," he said in an interview. "Why is Mr. Trudeau not paying back this trip? Why is he not being sanctioned in the House of Commons? Why is he not forced to appear before a committee and answer questions publicly?"

Both Mr. Kent and Mr. Cullen, who sit on the Commons ethics committee, said they want Ms. Dawson to return to the committee after her term ends on Jan. 8 to talk about the Trudeau report and offer her thoughts on modernizing the Act.

Ms. Dawson's detailed investigation released on Wednesday is raising questions about Mr. Trudeau's initial explanation to Canadians. As he defended his all-expenses-paid trip to the Bahamas earlier this year, Mr. Trudeau's stock answer was that he had simply been paying a visit to his friend.

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"Mr. Speaker, this was a family vacation to visit an old-time friend," Mr. Trudeau said in April.

However, the detailed investigation into his December, 2016, trip pointed out that the holiday was booked without any guarantee of the Aga Khan's presence at his residence.

"During the planning for the December, 2016 trip, the Trudeaus were informed that the Aga Khan and his family may or may not be present," the report said.

The Aga Khan was ultimately present on the island during that time-frame, Mr. Trudeau has said. However, the Commissioner's report added that during a previous trip in March, 2016, in which Mr. Trudeau's wife, Sophie Grégoire Trudeau, went to the island with friends, no members of the Aga Khan's family were present.

Mr. Cullen said it sounds like Mr. Trudeau was simply looking forward to an "awesome" vacation at someone else's expense.

"There is no way that could have been true," Mr. Cullen said of the Prime Minister's statements in the House.

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In response to the opposition attacks, the Prime Minister's Office said Mr. Trudeau's comments were made after the vacation had occurred and accurately represented what happened during the trip. In a news conference on Wednesday, Mr. Trudeau did not offer to pay any financial penalty in response to the Commissioner's report.

"As is the usual course, the Prime Minister reimbursed the costs of his, and his family's, flights to and from Nassau," PMO spokeswoman Chantal Gagnon said.

Mr. Trudeau long maintained he broke no rules because public-office holders are allowed to accept gifts from friends. But Ms. Dawson concluded the two men were not friends under the Conflict of Interest Act, having spoken only once in the 30 years before Mr. Trudeau became Liberal Leader.

"Justin Trudeau had no personal or private interactions with the Aga Khan and his family between 1983 and April, 2013, when he became Leader of the Liberal Party of Canada, except for his father's funeral in 2000," her report said.

The Aga Khan is the founder of the Aga Khan Foundation Canada, which was registered to lobby the federal government at the time of the vacations. Discussions were also under way over a $15-million federal grant to the endowment fund of the Global Centre for Pluralism, also founded by the Aga Khan.

"Because there was ongoing official business between the Government of Canada and the Aga Khan at the time each invitation was accepted, Mr. Trudeau, as Prime Minister, was in a position to be able to advance some of the matters of interest to the Aga Khan," Ms. Dawson said.

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It is the first time an Ethics Commissioner has found a sitting Prime Minister to have violated the Act since it was passed in 2006. While there is no official sanction against the Prime Minister, the negative findings stand to affect public perceptions.

"I should have taken precautions and cleared my family vacation and dealings with the Aga Khan in advance," Mr. Trudeau told reporters on Wednesday. "I'm sorry I didn't, and in the future, I will be clearing all my family vacations with the commissioner's office."