At least 1,000 people gathered on the steps and outdoor areas of Vancouver's art gallery to challenge the changes.
"It's been awhile since I've been to a rally that drew this many people. The square's full, said activist Jennifer Kuhl.
Reporter Jeff Harrongton interviews Jennifer Kuhl at C-51 protest
Kuhl says protesters believe Bill C-51 is dangerous, reckless and unacceptable.
"I think people are concerned about the impact that this will have on their individual freedoms and rights and they're concerned that the government has justified the ways that this would increase public safety.
So they worry it's mostly an attempt to restrict and silence dissent," said Kuhl.
A statement provided to the CBC by a spokesperson for Public Safety Minister Steven Blaney said the government "rejects the argument that every time we talk about security, our freedoms are threatened."
"Canadians understand that their freedom and security go hand in hand [and] expect us to protect both, and there are safeguards in this legislation to do exactly that," said Jeremy Laurin.
Bill C-51 impacts other legislation
Part 1 of the bill enacts the Security of Canada Information Sharing Act, which authorizes Government of Canada institutions to disclose information to other government institutions.
But there are also changes to the Secure Air Travel Act, the Criminal Code, the Canadian Security Intelligence Service Act and the Immigration Refugee and Protection Act. Most of the changes relate to a terrorism offence or activity.
In addition to the nationwide protests against Bill C-51, there are several online petitions gathering momentum as well.
On Friday federal New Democrat public safety critic Randall Garrison lashed out against C-51 saying many witnesses who have appeared before the government committee's have "highlighted serious problems with [it]."
"The bill is so bad that Canadians in over 50 towns and cities across the country will be rallying against it..."
Hearings on the bill will continue in Ottawa on Mar. 23.