A high-profile Canadian businessman is sounding the alarm over investments in the American pot industry after he was banned from entering the country for life.

"I was truly shocked by what happened to me," Sam Znaimer told CTV News.

Znaimer is one of Canada's best-known venture capitalists, having built his reputation investing in technology companies. Several years ago he started putting his money into budding pot companies and now gives speeches to ganja-preneurs and sometimes advises cannabis startups on how to best meet regulatory requirements.

Since news of Canada's pot bill passing made headlines around the world late last month, immigration lawyers have renewed their warnings that admitting to consuming marijuana could cause problems at the border, which is under federal jurisdiction. While marijuana is legal in several states, it remains an illicit and controlled substance federally.

But when Znaimer tried to cross in May, questions about his investments, not his personal consumption, landed him a lifetime ban from Canada's neighbour to the south.

"In the course of four hours, [Homeland Security] never did ask [about consuming marijuana] and I believe that was because they want to send a message to Canadians that it has not only to do with your personal behaviour, but whether in any way you have invested in these companies," Znaimer said.

U.S. immigration lawyer Len Saunders says Znaimer's experience isn't unique and could become more common as more people put their money into pot.

In one case, an Edmonton businessman was banned from the U.S. simply for being a part-owner of a Colorado building that leases space to a dispensary, Saunders said, adding some sobering advice for those looking to get into the industry: "Either stop travelling to the U.S. or get out of the business."

When it comes to marijuana, the term "business" can have a very broad definition, potentially including mutual funds or other investment plans connected to cannabis.

"What amazes me is this doesn't only impact people like me who are professionally involved, but there are thousands or tens of thousands of Canadians who have invested in companies with actives in the cannabis industry in the U.S.," Znaimer said.

There's little recourse for those who find themselves in Znaimer's situation. Banned travellers can apply for a waiver which costs $600 plus legal fees and only lasts for one to five years if approved.

So far, Saunders says it doesn't appear that investing in Canadian cannabis companies will land you in trouble at the border.

With files from CTV Vancouver's Penny Daflos