Canada's Supreme Court is hearing arguments Tuesday about a controversial measure known as security certificates.
The measure allows foreign-born individuals who are suspected security risks to be detained indefinitely if they refuse to be deported.
Three Muslim men are challenging the legality of the process. They were detained post-September 11 for alleged terror links.
The men - from Algeria, Morocco and Syria - say they are innocent and fear they will be tortured if they return home. They also say the government has not provided the evidence against them.
One suspect was released after about two years in custody. Another, who has been held for more than three years, has been ordered released.
The other suspect, who was detained in 2001, remains in custody, along with two other Muslim terror suspects who are not part of the challenge before the Supreme Court.
Canadian officials say the security certificate process is necessary to protect the country and used only in exceptional cases.
The arguments are expected to last three days.
The security certificates have been part of Canadian immigration legislation since 1978.
The developments come less than two weeks after authorities announced the arrest of 17 Muslims who allegedly planned a series of bombings and other al-Qaida-inspired terror attacks in Canada.
Some information for this report was provided by AFP, AP and Reuters.