Conservative Leader Andrew Scheer is refusing to explain how he travelled to the United States as a citizen without a valid U.S. passport.

Multiple requests to the party for an explanation have been ignored over the last 11 days.

The United States Immigration and Nationality Act says it is against the law for U.S. citizens — including dual nationals — to enter or leave the United States unless they are using a valid American passport.

Earlier in the campaign, Scheer confirmed he held dual citizenship in Canada and the United States, the latter passed to him by his American-born father. Scheer said his parents applied for the citizenship and a U.S. passport on his behalf when he was a child, but that he hasn’t renewed his passport since becoming an adult.

Story continues below advertisement

He is in the process of relinquishing his U.S. citizenship after filing the paperwork in August a few weeks before the campaign began. He said he intended to do so when he won the Conservative leadership, but did not get around to it for more than two years.

2:30 Trudeau: Scheer should have disclosed dual citizenship Trudeau: Scheer should have disclosed dual citizenship

U.S. passports are valid for up to 10 years, which means Scheer couldn’t have held a U.S. passport for at least the last 12 years if he hadn’t renewed it as an adult.

Members of Parliament can hold special passports for use on official Canadian business trips abroad, but the United States and Canada restrict their use for official business only and not personal travel. The United States requires special passport holders to apply for a visa for official business trips.

Former prime minister Stephen Harper tightened the rules for use of special passports in 2011 after stories emerged about their being misused for personal travel. The policies were changed to prevent their use for personal travel except by the Governor General, prime minister and their family members, and members of the Privy Council, which Scheer has been a member of since September 2017.

Story continues below advertisement

READ MORE: 3 federal leaders campaign in Montreal as election day nears

U.S. law still requires a visa to be obtained for official business trips even by the prime minister or Governor General.

The Conservative party has not offered an explanation for what passport Scheer used for travel, and when.

Scheer has discussed visiting the United States in recent years, both on family trips and getaways with friends on his quest to visit every NFL stadium in the country.

The Harper Conservatives were critical of former Liberal leader Stephane Dion and former NDP leader Tom Mulcair for holding dual citizenship with France when they were running for prime minister.

In 2005 Scheer also raised questions in a blog post about the dual Canada-France citizenship held by former governor general Michaelle Jean. He asked his constituents if that bothered them, and also asked if they felt it would be different if the second citizenship was American, but did not disclose at that time that he was also a dual national.

1:47 Scheer faces more questions over dual citizenship Scheer faces more questions over dual citizenship

Scheer rejected questions about that being hypocritical. He said he wasn’t hiding his American citizenship, but that “no one has ever asked” him about it.

Story continues below advertisement

He said “millions of Canadians have dual citizenship.”

According to Statistics Canada, the 2016 Census found 1.4 million Canadians hold a dual citizenship with another nation, including 340,865 people like Scheer, who are Canadians by birth but also hold a citizenship to another country.

The Census said 135,170 Canadians are dual citizens with the United States, second only to the United Kingdom with 152,060 dual Canadian-British citizens.