The Supreme Court of Canada began hearing a constitutional challenge Tuesday to the country's controversial terror law, which allows the country to detain non- residents deemed a security risk through the so-called security certificate process.

Three Muslim men are challenging the policy, arguing that detaining them for years if they refuse to return to their homelands violates Canada's constitution.

Mohamed Harkat, Adil Charkaoui and Hassan Almrei have all been held for years in jail because Canada's Security Intelligence Service alleges they have ties to al-Qaida although they say they are innocent.

The three people come respectively from Morocco, Algeria and Syria. They also challenge the conditions of their detention and the government's refusal to disclose evidence against them.

The Supreme Court is expected to hold three days of hearings to decide whether the certificates violate the Charter of Rights and Freedoms, as well as Canada's obligations under international human rights.

Since 1978, security certificates have been issued 27 times. They allow authorities to detain foreign-born nationals indefinitely without charge, and without making public any evidence against them.

The certificates have been receiving wide criticism with critics saying they deny people detained their Charter rights to due process under the law.

Matthew Behrens, head of the Campaign to Stop Secret Trials, accused Canada of implementing "two tiers of justice -- one of citizens and one for non-citizens."

Canada's Public Safety Minister Stockwell Day has expressed his support for the use of security certificates, and said he hopes the Supreme Court will uphold their use.

He said the security certificate process has been in place since 1978 and is used "very rarely." He also argued that those held under security certificates have options to either appeal, or to accept the deportation order.

Source: Xinhua