By Erwin Seba and Nicole Jao

PITTSBURGH (Reuters) - At a meeting of United Steelworkers union officials this week, presidential politics was off the agenda, a departure from past election-year gatherings and a sign of the division between USW members and union bosses over the candidates.

The leadership of the USW - a union of 1.2 million U.S. and Canadian workers from the steel, paper and energy industries as well as government workers - in July endorsed Democratic party candidate Kamala Harris, handing her an early victory just a day after President Joe Biden withdrew from the race against Republican Donald Trump.

But USW officials failed to mention Harris by name or ask the 300 local officials at a national oil bargaining conference to recommend members to campaign or vote for her. Still, attendees did see presentations about legislative proposals the union is pursuing in Congress and with the Biden administration.

The omission underscores the tensions within union ranks ahead of the Nov. 5 election, a race that polls show is essentially tied - leaving the outcome dependent on how union workers and others in battleground states vote. Union workers have traditionally formed a core part of the Democratic base but the dynamic has shifted in recent election cycles with Trump peeling away support from working-class, white voters.

Most oil workers come from states like Texas, Louisiana, Oklahoma and California that are not expected to be decisive in determining the outcome of the election.

Other major unions like the United Auto Workers have also backed the Harris campaign. But the powerful Teamsters union on Wednesday dealt a blow to her campaign by choosing not to endorse either presidential candidate.

The 1.3-million-member transportation workers union last failed to endorse a Democrat, President Bill Clinton, in 1996. The Teamsters released two surveys of rank-and-file membership that showed they prefer Trump over Harris.

Trump used the Teamsters survey results to proclaim he had won the Teamsters' rank-and-file endorsement.

The Harris campaign declined to comment. Her campaign has previously said that Harris will fight for union workers and if elected, would work with Congress to pass legislation making it easier to organize and "end union busting once and for all."

The oil-bargaining conference, just six weeks before the election, was also unlike prior conferences that featured dozens of members wearing pro-Trump MAGA red baseball caps. Attendees in Pittsburgh have been largely silent about the presidential election, only discussing it when asked by Reuters reporters.