Border officials have warned commuters that they risk losing any cash they're travelling with if they don't declare it.
An American commuter learned that lesson the hard way on September 24, according to U.S. Customs and Border Protection at the Ambassador Bridge in Detroit.
The CBP said the driver misrepresented the amount of cash they were bringing into the U.S., about $11,000 in American currency.
Border agents seized the cash, but allowed the traveller to continue on their way.
The CBP said the whole issue could have been avoided if the commuter was honest about the amount they were carrying, and if they had filled out a simple form.
To guard against money laundering, any amount over $10,000 must be declared. The requirement is the same in both the U.S. and Canada.
"There are no restrictions on the amount of money you can bring into or take out of Canada, and it is not illegal to do so, as long as you declare it," read the webpage from the Canada Border Services Agency. "This applies to all travellers, couriers, and to people carrying money on behalf of someone else."