Prime Minister Justin Trudeau held a rare weekend cabinet meeting and will speak with provincial leaders Monday over protests in Canada’s capital city that have entered their 18th day.

The protests against Covid-19 vaccine mandates, which include hundreds of semi trucks parked in the streets of Ottawa, swelled into the thousands over the weekend. But truckers were met on Sunday with counter-protests from residents who are angry that parts of their city have been paralyzed, with businesses closed and streets impassable, since the trucks arrived on Jan. 28.

The prime minister has faced pressure to use the military to end the demonstrations and has repeatedly said he thinks it’s a bad idea. However, in an interview with CTV News, Emergency Preparedness Minister Bill Blair said the government is prepared to use “emergency powers” if needed and characterized border blockades as a national security threat.

Under Canadian law, the federal government can enact emergency powers that allow it to prohibit travel within a specified area or remove personal property, while imposing fines or jail time on people contravening new orders.

The protesters are angry about rules that limit what unvaccinated people can do. A number of provinces have announced plans to get rid of Covid restrictions, but Trudeau has stuck with vaccine mandates that are under his government’s control—including those for federal government workers, air travelers and truckers entering the country from the U.S.

Protests have sprung up in other places, including the Ambassador Bridge between Detroit and Windsor, Ontario—the largest U.S.-Canada border crossing for commercial goods. The span was blocked for six days and was finally reopened Sunday night after police officers cleared out the demonstrators.

The reopening of the bridge, which carries about one-quarter of the commercial trade between the two countries, marks an end to the most economically-disruptive of the protests that have spread across Canada in recent weeks. At least six automotive plants were forced to cut output because of a shortage of parts, while shipments of everything from food to electronics was also hampered.

Ontario Premier Doug Ford declared an emergency on Friday, and police began clearing the protests Saturday morning in Windsor.