The government, saying the protests were damaging the economy and Canada's reputation as a reliable trading partner, introduced sweeping measures to support police forces and bring crowdfunding platforms under terror financing oversight.
The "Freedom Convoy" protests, started by Canadian truckers opposing a COVID-19 vaccinate-or-quarantine mandate for cross-border drivers, have drawn people opposed to Trudeau's policies on everything from pandemic restrictions to a carbon tax.
"The blockades are harming our economy and endangering public safety," Trudeau told a news conference on Monday. "We cannot and will not allow illegal and dangerous activities to continue."
Protesters blockaded the Ambassador Bridge, a vital trade route to Detroit, for six days before police cleared the protest on Sunday while others have shut down smaller border crossings in Alberta, Manitoba and British Columbia.
Frustration has grown with what critics see as a permissive approach by police to the demonstrations in the border city of Windsor, Ontario, and in Ottawa, the nation's capital, where protests entered a third week.
"Despite their best efforts, it is now clear that there are serious challenges to law enforcement's ability to effectively enforce the law," Trudeau said.
The 1988 Emergencies Act allows the federal government to override the provinces and authorise special temporary measures to ensure security during national emergencies. The law has only been used once before in peacetime, in 1970, by Trudeau's father, former Prime Minister Pierre Trudeau.
Earlier on Monday, four provincial premiers - in Alberta, Quebec, Manitoba and Saskatchewan - said they opposed plans to invoke the act, saying it was unnecessary.
Trudeau said the measures would be "geographically specific and targeted only to where they are needed". They will also be "time limited", he said.
The Canadian Parliament would have to approve the use of the emergency measures within seven days, and it also has the power to revoke them.
As well as providing police resources, Canada will broaden the scope of its anti-money laundering and terrorist financing rules to cover crowd funding platforms.
Finance Minister Chrystia Freeland said all crowdfunding programs and payment providers they use must register with Canada's anti-money laundering agency, FINTRAC, and report suspicious activities effective immediately.
The government will also allow banks to temporarily freeze the accounts of those suspected of supporting the blockades without obtaining a court order. In addition, the insurance of trucks involved in the blockades will be suspended.
Canadian authorities have said about half of the funding for the protests has come from US supporters.
