For union leaders, the Occupy Wall Street protesters seem like natural allies, even cheerleaders and enablers.

But controversy over a proposed oil pipeline has split the labor movement and alienated the liberal activists gathered in tent cities around the country.

The Occupy Wall Street group based in Manhattan’s Zuccotti Park approved a resolution on Sunday condemning a union-backed campaign that uses the 99 percent language to promote TransCanada Corp.’s plan to build a pipeline that would deliver oil harvested in Alberta, Canada, to the Gulf Coast.

“The leadership of the unions behind this campaign have made a public alliance with the oil industry and Tea Party funders,” the statement issued by OWS’ General Assembly said. “Big Oil and Tea Party billionaires are part of the 1 percent. The reference to the 99 percent is opportunistic and misleading.”

Now, Occupiers in Washington are considering passing a similar resolution.

The move is a reaction to a pro-pipeline advertising campaign — dubbed Jobs for the 99 — launched last week by the building trades department of the AFL-CIO and a labor committee established by the American Petroleum Institute. The push included print ads in Washington newspapers, radio spots in the states where the pipeline would be built, and a new website, jobsforthe99.com, the public manifestation of a years-long fight for the support of the Obama administration.

The State Department is reviewing the permit for the project, which TransCanada and the contracted unions say would yield 20,000 immediate private-sector jobs for their members.

Tom Owens, the director of communications for America’s Building Trades Unions, dismissed the charges, arguing that the union and the Occupiers are really on the same page.

The AFL-CIO has officially endorsed the Occupy movement, and last week National Nurses United joined Occupiers at the Treasury Department in Washington to demonstrate for a tax on Wall Street transactions. Labor unions sponsored a free cookout for participants in a general strike organized on the same day by Occupy activists in Oakland, Calif.

“It’s not like we are co-opting their message. Our message is their message,” Owens said. “I think it’s more hyperbole than anything else. … They want to use this issue [the pipeline] as leverage because they haven’t gotten other things they want from this White House.”

Five unions — the United Association of Journeymen and Apprentices of the Plumbing and Pipefitting Industry of the United States and Canada; the Laborers’ International Union of North America; the Teamsters; the International Union of Operating Engineers; and the International Brotherhood of Electrical Workers — have signed agreements with TransCanada to build the pipeline.

The issue has revealed a strategic division among union leaders and a battle for the support of the Occupy activists, who could become the basis for a young, protest-minded, grass-roots movement focused on the worker.

“It’s not our place to tell them what to do,” Thea Lee, deputy chief of staff for the AFL-CIO, told Roll Call. “But we are looking for the common ground, for the issues that resonate with them and also resonate with us.”

The AFL-CIO has not taken a stand on the issue, but others such as the Amalgamated Transit Union and the National Domestic Workers Alliance have come out in opposition to the pipeline, a decision that reflects a larger effort among labor leaders to embrace a more issue-focused agenda.

“Some of us were very much offended to see that this industry group — sponsored by Big Oil — was trying to use the ‘We are the 99 percent’ slogan,” said Bruce Hamilton, president of the Amalgamated Transit Union Local 1700. “We just can’t keep on supporting every single environmentally destructive project that the bosses come up with.”

Robby Diesu, a member of the training committee for Occupy DC, which helped stage an anti-pipeline protest with environmental groups at the White House on Sunday, said the division seemed generational.

“I think that a lot of that comes from the upper old guard of the unions,” Diesu said. “My friends who work for the unions completely oppose this pipeline.” He said the jobs are not worth the environmental consequences.

Several of the nation’s biggest unions — the Service Employees International Union, the American Federation of State, County and Municipal Employees and others — have not taken a side on the pipeline.

For the past decade, unions have struggled to balance the needs of their employers with the sympathies of their members, said Sean Sweeney, who directs the Global Labor Institute at Cornell University and helped write a report that found the pipeline would produce far fewer jobs than the industry claims.

“Ever since then it’s been a roller coaster of contradictions,” said Sweeney. “It’s a contradiction that they have to grapple with. In the meantime, they are losing friends in the Occupy Wall Street movement.”

Eliza Newlin Carney contributed to this report.