Press freedom and civil liberties groups on Tuesday mounted a legal challenge against Canada's recently passed anti-terror law, arguing that it poses a "grave threat" to the constitutional rights of citizens.

"The legislation presents disturbing implications for free speech, privacy, the powers of government ...and the protection of civil liberties in Canada," the Canadian Civil Liberties Association (CCLA) and Canadian Journalists for Free Expression (CJFE) said in a joint press statement.

The groups filed the legal challenge in the Ontario Supreme Court on that grounds that specific sections of Bill C-51 violate the country's Bill of Rights, known as the Canadian Charter of Rights and Freedoms, "in a manner that is not justified in a free and democratic society" and thus "must be struck down as unconstitutional and of no force and effect."

Despite the hundreds of thousands of Canadians who protested the bill, and widespread vocal opposition—from civil society, privacy, law and civil rights experts, prominent civil servants, academics, former Supreme Court justices, and former Canadian prime ministers—it was enacted on June 18, 2015.

Initially proposed by Prime Minister Stephen Harper as a means to supposedly "disrupt terror plots," the bill broadens the mandate of the Canadian Security Intelligence Service (CSIS) and amends over a dozen Canadian laws so that government agencies can more easily share private personal information. Critics say many of its provisions compromise the rights and freedoms of citizens, and can be used to target activists and protesters without an official permit or court order.

"Bill C-51 is a grave threat to our rights in Canada. It will lead to censorship and a massive chill on free expression, and enables a potentially widespread abuse of power," said Tom Henheffer, executive director of CJFE. "It unjustifiably infringes on the rights of all Canadians without making our country any more secure, and must be struck down."

And Sukanya Pillay, executive director and general counsel of the CCLA added that, because of the secretive nature of Bill C-51, "the public may never know if and when Canadians' rights are being violated, though individuals will be faced with the fallout."

Constitutional attorney Paul Cavalluzzo, who is helping the groups appeal the bill, told the Toronto Star that the charter challenge will focus on five sections of the legislation. The Star reports:

They say the bill attempts to give CSIS the ability to get a warrant in secret that pre-authorizes violations of the charter. They draw issue with the fact that twenty-one Canadian agencies have the authority to share or exchange personal information without any accountability or transparency. They raise concerns about new provisions under the bill that give the government the ability to hold secret hearings relating to people the government is trying to deport and say the bill would limit the information available to special advocates working on behalf of the person being deported. They do not support Secure Air Travel Act legislation which authorizes the government to have a no-fly list with the names of Canadians and, according to Cavalluzzo, evaluates the appeals of people who have their name on list in secret without representing their interests before a judge. Finally, they do not agree with amendments to the Criminal Code which create a new offence of “promoting terrorism in general.” Cavalluzzo said the term is too vague and will limit journalists who write about national security.

With a crowdfunding campaign to support the legal action, Henheffer said he believes their challenge is "the best chance to kill the legislation."