An official for U.S. Customs and Border Protection (CBP) says Canadians could be banned for life from entering the United States if they use marijuana, despite the fact that it will soon become legal in Canada.
The official went on to say that simply working in Canada's growing marijuana industry, or even investing in marijuana companies, could also get someone banned.
Under the current rules, admitting to past drug use is grounds for a lifetime travel ban in the United States, but some people can apply for temporary waivers to enter the country.
Crossing from Canada to America with possession of marijuana is also illegal, and could result in a $5,000 fine, even if the U.S. state has legalized or decriminalized marijuana use.
Beginning October 17, Canadians will be allowed to buy marijuana from special retail stores for recreational use.
A study by the Canadian government found that "about 4.6 million Canadians or 16% of the population used cannabis" in the first half of 2018.
Thousands more Canadians already own stock in cannabis companies which are openly traded on the country's stock exchange.
But Todd Owen, the executive assistant commissioner for the Office of Field Operations at CBP, said the organization will not change its policies to match Canada's new laws.
Canadians working in the legal marijuana industry already complain they have been hit with lifetime bans from entering the U.S.
Owen says border officers will not ask every Canadian about marijuana use, but it might come up during a routine interview or car search at the border.
Staying silent when asked about marijuana could help a traveler avoid a lifetime ban, but it could also be used to deny them entry for that visit.
Legal experts worry that Canadians who own stock in a marijuana company through a mutual fund could unknowingly put themselves at risk of being blocked from entering America for life.
But Canada's Prime Minister Justin Trudeau said he would not press America to change its border policies earlier this week.
"Every country has the right to judge who gets to come into their borders or not," Trudeau said.
"I wouldn't presume to have any other country tell me how or who we can let into Canada. And I certainly won't work to assume or impress upon the U.S. who they have to let in or not."
"But there is no question that we are working with U.S. officials," he added, "they have legalized marijuana in a number of their states, and we're trying to make sure that travel between our two countries (is) not disrupted."
Trudeau also said that he had "never lied to a border guard."
So far just nine states and Washington, D.C. have legalized recreational marijuana use. The federal government still considers that use illegal.