SUNDRE, Alberta—This town nestled in the foothills of the Rocky Mountains is known for its annual pro rodeo in June, which includes a parade of cowboys and cowgirls on horseback, school marching bands and colorful floats celebrating the heritage of rural Alberta.

This year, a feud erupted over a proposed parade float festooned with Alberta provincial flags. Volunteer parade organizers rejected the idea as too political amid campaigning around a referendum on Alberta staying in Canada or moving toward independence—and were then met with an onslaught of harassment and online abuse from supporters of the float.

They reversed their decision, but the harassment continued. Other floats pulled out. Soon, organizers canceled the decades-old parade altogether.

The uproar reflects the bitter divide across Alberta ahead of a historic referendum Monday on whether it should remain part of Canada or take steps toward holding a second, binding referendum on separation. While the campaign has been relatively muted compared with past constitutional battles in Canada, the friction in Sundre shows the tensions bubbling below the surface.

“There will literally be marriages that break up over this, neighbors that don’t talk to each other, business partnerships that rupture, communities that get divided,” said Jason Kenney, a former conservative premier of Alberta who is leading a campaign to keep the province in Canada. “This is the political equivalent of a civil war.”Nathan McCullough, who runs a butcher shop in Sundre, was undecided about the referendum, which asks Albertans nine other questions, including whether the province should have greater power over immigration and the appointment of judges—all of which could foment tensions with the federal government.

On question 10, about Alberta’s status in Canada, McCullough says that while he isn’t sure he necessarily favors secession, he could see the benefits of voting for a second referendum to send a message of protest to the federal government in the capital, Ottawa. “It’s always the squeaky wheel that gets the grease,” McCullough said. And that sort of thinking has worried supporters of staying in Canada.

Polls show that an overwhelming majority of Albertans want to stay in Canada. A Leger poll this month found 70% support remaining. However, separatists remain committed regardless of the outcome, and federalists are concerned that voter complacency could tilt the result.

“It’s not an ordinary vote for [separatists],” Kenney said. “They’ll show up. They’ll crawl over broken glass.”The vote comes at a delicate time for Canada’s national unity as President Trump has imposed tariffs on Canadian goods and mused about making Canada the 51st state. In Quebec this month, voter discontent with incumbents led to separatists taking power, and they are promising their own independence referendum after Trump leaves office.

Prime Minister Mark Carney, who led the Bank of England during Brexit, has called the Alberta referendum a “dangerous bluff .”A prolonged debate over Alberta’s place in the current federation of 10 provinces and three territories could hamper his efforts to expand market access for the province’s oil and gas resources—part of his strategy to reduce Canada’s economic reliance on the U.S.

After months largely on the sidelines, Carney in recent days has traveled across the province to campaign and urge Albertans to vote to stay in Canada, saying the referendum couldn’t come at “a worse time.”

“The world has become more dangerous and divided,” he said at a federalist rally in Calgary on Thursday. “Some outside our borders are working to break us so they can own us.”Alienation in Alberta is longstanding. When Alberta and Saskatchewan joined the confederation in 1905, the federal government retained control over their natural resources until 1930, unlike the original four provinces. That dynamic created a lingering perception that eastern Canada exploits the west’s resources while scorning its residents.

Tensions flared again under former Prime Minister Justin Trudeau, whose environmental policies drew fierce pushback from Alberta, home to the world’s fourth-largest proven oil reserves. Equalization transfers—where federally collected taxes fund public services in poorer provinces—have also remained a sore point, as prosperous Alberta hasn’t received payments in six decades.

Today’s separatist movement is driven by both historic grievances and newer populist themes. In towns across the province, separatist leader Mitch Sylvestre has campaigned for leaving Canada and against federal energy and immigration policies while casting doubt on Covid-19 pandemic-response measures and making conspiratorial claims about Ottawa.

Jared Wesley, a political scientist at the University of Alberta, said the current movement mirrors right-wing populist campaigns like Brexit and the MAGA movement in the U.S.

“It’s a mistake to look at it as a simple offshoot of our grandparents’ western alienation,” Wesley said.

Separatist leaders have also reached out to U.S. officials for support. Jeffrey Rath, a separatist leader, says he is “gratified by the expression of enthusiasm” from American contacts. The White House said it offered no commitments, while the State Department noted the vote is a decision for Albertans.

Alberta Premier Danielle Smith, who describes herself as a federalist and has sought greater autonomy for her province from Ottawa, called the referendum in May. Critics argue the move was meant to pacify divisions and prevent a mutiny within her United Conservative Party, where roughly half of voters favor separation.

“[Separatists] were basically daring her to do this,” said Darrell Bricker, chief executive of pollster Ipsos.

Economic warnings about separation have intensified. A Calgary Chamber of Commerce survey found that nearly half of member respondents would consider relocating if voters opted for another referendum. A report commissioned by the provincial government estimated that creating an independent nation could cost up to $120 billion (reported as 170 billion Canadian dollars) over five years, lower wages, raise the unemployment rate and reduce long-term economic output by up to 16%.

Then there are the social costs to a divisive, monthslong debate over the province’s future in Canada that are harder to calculate and could linger well after the ballots are counted.

In Sundre and across Alberta, residents lament that the political debate had poisoned a cherished tradition such as the rodeo parade and that symbols such as the Albertan and Canadian flags have become so politicized.

Art Bryson-Hare, who moved to Sundre 30 years ago from Nova Scotia, said he was uncertain about the rodeo committee’s decision to cancel the parade over the flag float.

“I’m not really sure how political flying our Alberta flag is,” he said. “It was just a float.”