Canadian immigration authorities say they have detained dozens of people ferried over the border by Romanian people-smugglers.
The 30 people held were part of a group of 85, all from one Romanian district, who went to Mexico, then illegally crossed into the US and Canada.
All have been classified as "irregular arrivals" under tough new refugee legislation.
The 85 Romanian nationals arrived from the US on five different dates in 2012.
They crossed the border between Vermont and Quebec, then claimed asylum.
Thirty have been arrested, 10 have received letters advising them they have been designated irregular arrivals, and the remaining 45 have not been found.
Some 35 of the 85 are children, reports the National Post newspaper.
"Our doors are open to immigrants to Canada who follow the rules and wait in line, but we have no tolerance for those who abuse our generosity or cheat the system to jump the queue," Immigration Minister Jason Kenney said in a statement.
"Today, we are sending a strong message to those who are thinking of using the services of criminal human smugglers to sneak their way into Canada - don't do it."
Irregular arrival status forbids the holder from applying for permanent residency for at least five years.
Smuggling rings often entice people with the promise of good jobs, but those ferried over borders often end up owing large debts.