Canada is moving toward legalizing recreational marijuana, while four U.S. states, two of them border states, already have.

On Tuesday, four more states voted to allow recreational marijuana. One, Maine, also borders Canada.

READ: Four more states vote to legalize recreational marijuana

Despite both countries becoming more permissive about pot, though, admitting at the U.S. border that you’ve smoked marijuana — ever — can still get you barred from the United States for life. That’s true even if you’re crossing into a state, like Washington, that allows recreational marijuana.

And it may continue to be true after Canada legalizes recreational marijuana, even if you waited until it was legal to smoke it, a lawyer warns.

A provision in U.S. immigration law which bars “drug abusers” on medical grounds applies even if you used marijuana in another country legally, explains Bellingham, Wash.-based immigration lawyer Scott Railton.

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“Even though it wouldn’t be against the law under a foreign jurisdiction, the substance is still listed as a controlled substance under U.S. law. That would be the concern.” Tweet This

To be admitted, you would have to be screened by a doctor approved by the U.S. government.

Jessica Goldstein, a 33-year-old White Rock, B.C., woman, unknowingly triggered an expensive bureaucratic ordeal in 2013 as she tried to cross the border to go to a concert.

“As we were crossing the border, they started asking us if we had ever used any drugs,” she remembers. “I thought I was being honest, I wasn’t breaking any rules, and I said I’d smoked pot before.”

“After that we got pulled in for questioning, and got questioned for about six hours. It was very intimidating. After the first two or three hours, I’d say whatever just to get out of there. There was a lot of sitting and waiting as well.” Tweet This

In the end, Goldstein was barred from the U.S. for admitting prior drug use, and has had to apply for a series of waivers to be allowed in.

“If it looks like the individual is a recreational user, maybe they have a picture of a marijuana leaf somewhere, then a lot of times that raises the question,” says Buffalo, N.Y.-based immigration lawyer Fadi Minawi of Niren and Associates. “Depending on the reason that the person is going to the U.S., a concert or something else, they might be questioned as to their previous history.”

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In recent years the firm has handled over 50 cases of people barred from the U.S. because of admitting a history with pot but want a waiver to enter anyway, he says.

It’s not an easy path — the waiver applications can take a year to process and cost $US640 to file — soon to rise to $US930. Lawyers’ fees can add another $US2,000 to that, Minawi says.

“There were some embarrassing things,” Goldstein says. “I need to get a letter of reference from my employer, as well as character references from stand-up citizens in the community. I don’t feel that it’s anybody’s business but my own, really.”

And the waivers are good for only a limited period — the most generous for five years, at which point the process has to begin all over again. If you want to keep crossing the border, in principle it will continue for the rest of your life.

READ: How will legal pot be sold? Three things that might happen, and one that won’t

Some are for shorter periods — Goldstein’s first was for a year, and her next for two years. That one hasn’t expired yet, but she’s hoping to get a new one approved before the fee increase kicks in.

For every waiver, Goldstein has to go through the whole process — lawyers, fees, awkward workplace discussions and all — all over again.

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“You have to get new ones, and of course my employer has changed a couple of times over the course of four or five years.”

She says the process has cost her about $2,000.

U.S. border guards have been barring Canadians from entering the States for answering “yes” to having used marijuana. Immigration lawyer Len Saunders spoke with Geoff Hastings on BC1 about what you should do if you are asked about your pot use.

7:16 Border pot problems predicted to get worse Border pot problems predicted to get worse

A lot depends on the personality and opinions of the border guard you end up with, Railton says.

“Sometimes this marijuana question is prompted by individual officers rather than policy. But once it gets going down that road, supervisors will uphold the officer asking the questions.”

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Goldstein says she witnessed this first-hand — a few weeks before she was banned from the U.S., a border guard asked her then boyfriend if he had ever smoked marijuana. He admitted it, and was waved through.

In a 2015 poll, 18 per cent of Canadians surveyed said they had used marijuana in the previous year, which works out to about 5.4 million people.

If you’re caught in the situation, Minawi says, remember that you don’t have to answer the question. While this will probably get you refused entry, it shouldn’t have long-term consequences:

“If the individual is turned away at the border for simply not answering the question, it still better than admitting to the elements that make it a crime and being barred for life. It’s not illegal to not answer a (Customs and Border Patrol) officer, but it’s up to the CBP officer’s discretion to turn you away at the border.”

Railton agrees: “The cost of applying for waivers for the rest of your life is pretty expensive. In due time you could make another application for admission, and it probably wouldn’t come up.”

Lying, however, is a poor idea, Minawi argues: “Lying can carry a bar for life, in and of itself.”

READ: Canada looking to change policy that bans marijuana users from the U.S.

In early September, Public Safety Minister Ralph Goodale said the U.S. border rules created “a ludicrous situation,” and pledged to raise it in future talks with American officials.

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Prime Minister Justin Trudeau, who publicly admitted marijuana use in 2013, would be at risk of being banned from the U.S. if he wasn’t a head of government.

We asked a U.S. Customs and Border Patrol spokesperson for statistics about how many Canadians have been barred from the U.S. for past marijuana use and how many have been given waivers, but didn’t get a response.