If you鈥檝e 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鈥檚 questions about your marijuana use could have serious consequences.

鈥淚t鈥檚 basically black and white 鈥 if you admit to a U.S. border officer at a U.S. port of entry that you鈥檝e smoked marijuana in the past, whether it鈥檚 in Canada or the U.S., you will be barred entry for life to the United States,鈥 immigration lawyer Len Saunders told CTV鈥檚 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 , 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鈥檚 not advising Canadians to lie to U.S. border officials, but said they simply don鈥檛 have to answer when asked if they鈥檝e ever smoked pot.

鈥淎s a Canadian citizen at a U.S. point of entry, you have the right not to answer that question,鈥 he said.

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

He said he鈥檚 had clients who鈥檝e 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.

the Canadian government warns travellers that 鈥減revious use of cannabis, or any other substance prohibited by local law, could result in a traveller being denied entry to their destination country.鈥

鈥淓ach 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鈥檚 entry or exit requirements,鈥 the warning says.