() Canada has changed its rules for traveling to the United States amid concerns surrounding some of President Donald Trump’s policies. 

Starting April 11, Canadians who will be in the United States for more than 30 days will have to register with United States authorities. If they don’t, it could result in “penalties, fines and misdemeanors,” according to the advisory. 

This rule was previously unenforced, the Vancouver Sun reports. 

Newsweek writes that this advisory update comes as Canadian and other foreign tourists have been detained at the U.S. border over visa concerns and documentation mismatches. 

People have also had issues with passports because of an executive order from Trump that requires the documents to reflect the sex a person was assigned at birth. Axios reports that European countries such as Finland, Denmark and Germany also have warned people to exercise caution in their travel advisories for any transgender and non-binary people who want to go to the U.S.

Adding to the tension between Canada and U.S. are the trade war between the two, as well as Trump’s repeated remarks that Canada should be the 51st state.

Former Canadian Prime Minister Justin Trudeau urged those from Canada to stay in the country for vacations in a speech last month, The New York Times reported. 

Statistics Canada writes that the number of Canadians returning to the United States by car went down 23% in February. It said Canadian residents flew back from 585,700 trips to the United States in the same month, a 13.1% decline from last year. 

Harold White, 72, who lives in Quebec, told the New York Times that he decided that he will no longer be traveling to the United States unless it’s “absolutely necessary.”

“It pains me to think that I’m not going to Maine or to Cape Cod or even to New York City for a vacation in the near term,” White said. “But this time around, really, I feel like Canadians have been slapped across the face by Trump.”

The Associated Press contributed to this report.