Ottawa (AFP) - Lawmakers are expected to pass an anti-terror statute Wednesday granting Canada's spy agency sweeping new powers criticized by civil rights advocates.

The final reading of the bill after several failed opposition attempts to water it down in recent days follows two deadly attacks in Canada last year.

It will mark the the biggest overhaul of Canada's anti-terrorism legislation since 2001, when Ottawa rushed through new national security measures following attacks in the United States.

A government spokesperson told AFP the House of Commons vote is scheduled for Wednesday evening.

The bill is assured to pass with the support of Prime Minister Stephen Harper's Tory parliamentary majority, before it is granted royal ascent likely in June.

The updated act would criminalize the promotion of terrorism, make it easier for police to arrest and detain individuals without charge, and expand the Canadian Security Intelligence Service (CSIS)'s mandate from intelligence-collection to actively thwarting terror plots and working outside of Canada for the first time.

The law was introduced following a lone gunman's October 22 killing of a ceremonial guard and storming of parliament in Ottawa, and the hit-and-run murder of another soldier in rural Quebec the same week.

Ottawa has also held it up as yet another policing tool needed to stem a tide of young Canadian men and women travelling abroad to join the Islamic State group.

At least six Canadians have died over the last two years fighting alongside extremists in Syria and Iraq.

As part of CSIS's new mandate, the agency could intercept financial transactions, prevent a suspect from boarding a plane, intercept weapons or conduct "online counter-messaging," for example, by hacking a Twitter account used to recruit jihadists.

The government has insisted the new measures target "terrorists" and not law-abiding citizens.

But the act has been sharply criticized by former prime ministers and top judges, civil liberty, free speech and privacy advocates, aboriginals and environmentalists who fear being targeted by police, and a topless protester.

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A petition against the bill has also garnered more than 200,000 signatures.

Leader of the opposition New Democratic Party, Thomas Mulcair, has said the measures are lacking in oversight and a danger to Canadians' constitutional rights.

Prime Minister Stephen Harper's Conservatives "are going too far in eroding our way of life with their new anti-terrorism law," said the NDP.

He was echoed by National Chief Perry Bellegarde of the Assembly of First Nations who said the bill sets out an "overly broad" definition of activities that could undermine national security.

Bellegarde warned that aboriginals agitating for their treaty rights could be "labelled as threats" and find themselves under surveillance for political activism.

He pointed to leaked federal police documents that lumped "violent aboriginal extremists" in with militant environmentalists and others willing to go beyond peaceful actions to advance their cause.

Protests were held across Canada to back those concerns.

In March, a member of the Paris-based radical feminist protest group Femen also removed her top and screamed in the House of Commons that the anti-terror law was a "war on freedom."