TYENDINAGA, Ontario — A dilapidated snow plow, three tents and some barrels sit beside the snowy tracks of the Canadian National Railway in Tyendinaga, Ontario, a protest in support of Indigenous leaders trying to stop the construction of a gas pipeline thousands of miles away, in British Columbia.

The blockade, set up by the Mohawks of Tyendinaga, may not look imposing. But the barricade, and similar ones erected at transport points across the country, has disrupted travel for Canadians since last week — and drawn attention to the pipeline dispute.

Tens of thousands of travelers have had to scramble after rail service was halted between Toronto and the cities of Montreal and Ottawa. Hundreds of freight trains have been stalled, and ports in eastern Canada have been isolated from the rest of Canada and the United States. Factories have braced for closing because of delivery interruptions.

On Wednesday, Prime Minister Justin Trudeau weighed in for the first time, calling on all sides “to resolve this as quickly as possible.”

“Obviously it’s extremely important to respect the right to freely demonstrate peacefully,” Mr. Trudeau told reporters in Senegal, one of a series of official stops he is making in Africa. “But we need to make sure the laws are respected.”

Since he was first elected in 2015, Mr. Trudeau has tried to balance his promises to reconcile with Canada’s Indigenous people for past wrongs and to take Canada toward a carbon-neutral future — all while maintaining the country’s economically important oil and gas industry.

This dispute, though, is largely unfolding under the jurisdiction of the provincial government in British Columbia.

Both British Columbia and the elected band councils of the Wet’suwet’en First Nation in the province — the leadership established under Canadian law — have signed onto the 416-mile pipeline project, which links gas wells in the British Columbia interior to a new liquefied natural gas terminal on its coast.

The company building the pipeline, which will cost 6.2 billion Canadian dollars, has promised hundreds of millions of dollars in contracts to Indigenous businesses.

But another branch of the Wet’suwet’en’s leadership, the hereditary chiefs, says the pipeline would alter their traditional lands; they have been protesting in an encampment at the construction site for more than a year.

Last week, the police, acting on a warrant, tried to remove them, inspiring protesters across the country to act in sympathy and set up their own blockades, as well as campsites, at transport sites, beginning with the one in Tyendinaga.

The protesters appear to be an informal alliance of environmentalists and Indigenous rights proponents. They have mired traffic in Vancouver, British Columbia; snarled ports in and around that city; and shut down another Canadian National line in the north of that province.

Sit-ins have been staged at politicians’ offices throughout Canada. A commuter rail line that runs through Mohawk land to Montreal remained blocked on Wednesday and sporadic demonstrations have been held across the country.

Less than 24 hours after the protest began last week in Tyendinaga, a court granted the railway an injunction ordering the demonstrators to leave. But how and when that order will be enforced is unclear.

“It’s not just passenger trains that are impacted by these blockades, it’s all Canadian supply chains,” said J.J. Ruest, the president and chief executive of Canadian National, in a statement. “C.N. will have no choice but to temporarily discontinue service in key corridors unless the blockades come to an end.”

Via Rail Canada, the passenger service, has canceled all trains from Toronto to Montreal and Ottawa, at least until Saturday.

At the tracks in Tyendinaga, surrounded by snowy fields, several Mohawk protesters pointed with pride to the west where a long freight train had idled for six days.

They had little or no sympathy for complaints from rail passengers, or for the fear that the protests will create economic problems. They all declined to give their full names because they face the prospect of arrest as well as being sued by the railway. But one man who identified himself as Bill said he hoped the protests would make people “aware of what’s going on, maybe it will make them think.”

For him, the protest is about Indigenous land rights. Like several of the protesters at the tracks, he vowed to stay until the pipeline project, known as Coastal GasLink, is canceled.

Others said the pipelines would pollute waters and land.

On Tuesday, two officers of the Ontario Provincial Police — carrying a ceremonial gift of maple syrup, which was declined — arrived to meet with protesters. Later in the day, two other officers arrived, this time without gifts and wearing protective vests and utility belts under their civilian parkas.

Their message was blunt: The situation created by the protest had become “dire” and the police were preparing to enforce the court order.

The only effect of that was an effort to make the protest appear more intimidating.

The snow plow, which suffers from a pronounced hydraulic fuel leak, was started up, its lights turned on and the plow blade raised. Two cars, their headlights lit, were also aimed down toward two police cruisers sitting several hundred yards away. A few protesters stood in front of the tracks.

On Wednesday, there was another official effort to end the disruptions — this time by local Mohawk authorities. The chief of the area’s Indigenous police force, Jason Brant, urged everyone to pack up, noting that the rail shutdown was leading to layoffs.

“Today is the day to go to your own beds — the point’s been made,” Mr. Brant said.

But there was no sign that the group was backing down. One tent and an aging former school bus were moved further east — to form a second protest site.