Canadian officials say they are monitoring a ship carrying Sri Lankan asylum seekers as it heads towards its west coast.
Public Safety Minister Vic Toews said there was reason to believe that members of the defeated Tamil Tigers movement were on the Thai ship.
The Tamil Tigers have been outlawed in Canada as a terrorist group since 2006.
The MV Sun Sea is due to reach British Columbia on Canada's Pacific coast in the next few days.
"I can assure you that we are concerned about who is on that ship and why they might be coming," Mr Toews said in a speech in Toronto on Monday.
He highlighted seaborne human smuggling as a major national security concern.
"It is important to send a message that Canada should not be viewed as an easy entry into North America and that we are very concerned about security issues," Mr Toews said.
"The problem of human smuggling and illegal migration is a serious one, and the abuse of our immigration system is something that our government will not tolerate."
The US Coast Guard is also reported to be monitoring the ship.
Two local prisons were preparing to make room for the refugees, said John Leeburn, a spokesman for the District of Maple Ridge outside Vancouver.
Corrections officers and sheriffs at the prisons have been told to be ready for up to 500 Tamil migrants or refugees in the coming days, most of them men, AP news agency reported.
The Tamil Tigers were defeated by the Sri Lankan army last year after more than two decades of war.