As a sweeping anti-terrorism bill winds its way through Parliament, former prime ministers and former Supreme Court judges are expressing concerns that Canada’s security agencies don’t have adequate checks and balances.

Last week, Parliamentarians debated Bill C-51, which gives more sweeping investigative powers to Canada’s security agencies, including the Canadian Security Intelligence Service.

Opposition Leader Tom Mulcair said last week that the NDP will not support the legislation, calling it “dangerous” and “over-reaching.”

The NDP are not the only ones concerned that the legislation does not boost oversight of Canada’s spy agency.

In an open letter published last week by The Globe and Mail, former prime ministers Joe Clark, Jean Chretien, John Turner and Paul Martin called for more accountability and independent oversight for the country’s security agencies.

The prime ministers said that a “lack of a robust and integrated accountability regime” makes it difficult to “meaningfully assess the efficacy and legality” of the country’s security activities. This absence, they said, could ultimately lead to problems around public safety and human rights.

Former Supreme Court Justice John Major, one of the letter’s signatories, told CTV’s Question Period that he’s “puzzled” at the government’s “reluctance” to ensure oversight.

“When we speak of oversight, I don’t think any of us think the agencies are going to deliberately extend their reach. But the fact is they have a job to do, they think it’s important, they get over-enthusiastic when they think they’re hot on the trail of something, and it’s very easy to slip over the edge,” Major said. “We’ve seen it with police forces, we’ve seen it in the past with CSIS.”

Speaking on Question Period, Defence Minister Jason Kenney said that the government is providing protection to civil liberties by ensuring that the additional powers being proposed are vested in the courts.

“The security agencies can go and obtain orders to interrupt potential terrorist activities, to detain a suspected terrorist for up to seven days, but they can’t do it on their own, it requires the approval of a judge,” Kenney said.

However, Major says there is little worry about procedures where warrants must be granted by a judge.

“There’s a wide range that these agencies, day-to-day, are engaged in, and it’s that part of their activities that’s outside courts and provisions that draws some concern,” Major said.

Critics are also asking why government doesn’t implement parliamentary oversight, similar to U.S., U.K. and Australian systems. Kenney said that the Conservatives feel a “non-political approach” is more appropriate.

“And that’s what governments before have felt as well,” Kenney said. “That an objective, independent group of experts that are not part of Parliament or politics should be taking a look at the operations of CSIS.”

Former Supreme Court Justice Michel Bastarache, who also added his name to the open letter, says there are models that experts feel are superior to Canada’s system.

“I think what we’re saying is, why not examine what we have in light of what exists elsewhere and see whether we have the best system possible to ensure confidence of the public in the system, but also the image of Canada throughout the world,” Bastarache told Question Period.