OTTAWA—With bombings abroad and a terror plot at home, MPs have voted to give Canadian security officials “exceptional” powers to probe potential terrorist acts — powers that critics say trample on civil liberties.

Anti-terror legislation passed Wednesday will enable preventive arrests, meaning Canadians can be held for up to three days without charge. And it opens the door to investigative hearings, where people can be compelled to testify under threat of detention.

The Conservative government says the measures contained in Bill S-7, the Combating Terrorism Act, are vital to assist law enforcement officials to foil unfolding terror plots.

The bill passed 183-93 with the Liberals joining the Conservatives to support the measures. New Democrats opposed it.

“Terrorism and violent extremism are real threats to Canada,” Public Safety Minister Vic Toews said in a statement.

“Bill S-7 will provide additional tools for law enforcement to help in the investigation of terrorism offences and thereby help to protect the safety of Canadians.”

The law also makes it illegal to leave Canada or attempt to leave the country to commit a terrorism offence, such as attending a terrorist training camp or engaging in other terrorist activities.

But civil liberties groups and some politicians say the police powers go too far, creating the potential for secret inquisitions and unfair detentions.

“We don’t feel this has the proper balance between protecting rights and the things we need to do to prevent terrorism,” said NDP MP Randall Garrison, the party’s public safety critic.

Garrison said the government’s focus should be on boosting frontline resources, such as the RCMP and the Canada Border Services Agency, which are both being squeezed by shrinking budgets.

He said police have conducted successful terror investigations — including Monday’s break-up of an alleged plot to attack a Toronto-bound train — without these special powers.

“We don’t need extra legislative measures to do this. When people are given the resources in law enforcement and security agencies, they can produce the results,” Garrison said.

Preventive arrests and investigative hearings were both introduced by the Liberals in the wake of the 9/11 terror attacks but had lapsed under a sunset clause in 2007.

The new law revives the two measures, despite the concerns of civil liberty groups that they threaten basic freedoms.

“Renewing these provisions would normalize exceptional powers inconsistent with established democratic principles and threaten hard-won civil liberties,” an alliance of organizations said in a statement.

They include the Canadian Civil Liberties Association, the British Columbia Civil Liberties Association and the Canadian Council on American-Islamic Relations.

The groups said even the need for the measures is in question, saying that during the previous time they were in force, they were never used once for their intended purpose.

“Every major criminal terrorism-related incident in Canada since 2001 has been disrupted and prevented without the need for preventive detention or investigative hearings,” their release said.

The bill was brought back to the Commons for final debate on Monday, the same day the RCMP announced it had arrested two men who allegedly wanted to derail a train running between Toronto and New York.

The government has denied the arrests were timed to bolster support for its legislation. Still, Garrison said the arrests, combined with last week’s fatal bombings at the Boston Marathon, have created an emotional backdrop for debate.

“I think the government was hoping that at a time of heightened emotions, people might not look so closely at the bill,” Garrison said.

Liberal MP Bob Rae says his own work in investigating the aftermath of the 1985 bombing of Air India Flight 182 that killed 329 passengers and crew convinced him that new steps were justified.

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“We have to take the events of recent years seriously. We can’t pretend they haven’t changed some of the threats we face,” Rae said in an interview.

“I think what is being proposed is reasonable and proportionate to the potential threats that are very much out there,” he said prior to the vote.

“We have to provide the necessary protections to Canadians.”