If you’ve ever smoked pot in your life, you may want to think twice about answering certain questions at the U.S. border on your next trip south.

Even though recreational marijuana is legal in several U.S. states and will be legal across Canada on Oct. 17, possession of marijuana is still a criminal offence under U.S. federal law.

That means that answering a U.S. border officer’s questions about your marijuana use could have serious consequences.

“It’s basically black and white – if you admit to a U.S. border officer at a U.S. port of entry that you’ve smoked marijuana in the past, whether it’s in Canada or the U.S., you will be barred entry for life to the United States,” immigration lawyer Len Saunders told CTV’s Your Morning on Tuesday.

Saunders, who is based in Washington state, said that Canadians who get the lifetime ban can still apply for temporary waivers, which can allow them to cross the border for up to five years.

But they will have to keep re-applying to get those waivers for life and the process can be lengthy and costly.

According to the U.S. Customs and Border Protection website, an application for a waiver of inadmissibility costs US$585 and can take up to a year to process. The application requires a lot of paperwork, which may include fingerprinting and a verification of your criminal record.

Saunders said he expects U.S. border officers will be asking Canadians more frequently about cannabis use once pot is legal here.

He’s not advising Canadians to lie to U.S. border officials, but said they simply don’t have to answer when asked if they’ve ever smoked pot.

“As a Canadian citizen at a U.S. point of entry, you have the right not to answer that question,” he said.

Those who refuse to answer the question may be denied entry to the U.S. that day, but it’s better than being slapped with a lifetime ban, Saunders said.

He said he’s had clients who’ve told him they were threatened with lie detector and drug tests, but those are not allowed at the border.

According to Statistics Canada, 49.4 per cent of men and 35.8 per cent of women admit to using marijuana at some point in their lives.

On its website, the Canadian government warns travellers that “previous use of cannabis, or any other substance prohibited by local law, could result in a traveller being denied entry to their destination country.”

“Each country or territory decides who can enter or exit through its borders. The Government of Canada cannot intervene on your behalf if you do not meet your destination’s entry or exit requirements,” the warning says.