Maine union organizers say a misunderstanding of national rules governing candidate endorsements led to the cancellation of Sen. Bernie Sanders’ planned Labor Day speech.

The Democratic presidential candidate had been billed as the keynote speaker at the annual Labor Day breakfast in Portland hosted by the Southern Maine Labor Council, a local affiliate of the AFL-CIO that represents some 5,000 workers in York, Cumberland and Sagadahoc counties.

Andy O’Brien, a spokesman for the Maine AFL-CIO, said Tuesday that local organizers were unaware of national AFL-CIO rules that prevented Sanders from being invited to speak at the event.

“He canceled because the national AFL-CIO has strict rules regarding its endorsement process,” O’Brien said. “This includes not allowing presidential candidates to speak at state federation or central labor council events unless all of the candidates are invited.”

The concern, O’Brien said, was that Sanders’ appearance would look like an early endorsement by the AFL-CIO, which includes some 12 million active and retired workers and is the largest labor federation in the United States. It doesn’t typically endorse candidates in presidential races – although member unions may.

Sanders, who had been informed Friday that he could attend but not speak at the breakfast Monday, arrived in Portland on Sunday night and delivered a speech to more than 1,600 supporters packed into a rally at the State Theatre. It wasn’t until just after 1 a.m. Monday that the media were notified that Sanders would not appear at the breakfast.

Sanders’ campaign had planned the two events in Portland as part of a two-day sweep into Maine and New Hampshire over the holiday weekend. After the Sunday evening rally and skipping the breakfast event in Portland on Monday, Sanders continued with his plans to walk in a Labor Day parade in Milford, New Hampshire, later in the day.

On Tuesday, Southern Maine Labor Council President Doug Born said that he simply “missed the memo” that national leaders sent out in May reminding local council leaders that they could not have single candidates speak at their events for fear it would look like an endorsement of that candidate.

Born said he addressed the crowd Monday about what he called, “the 800-pound gorilla” in the room – Sanders’ absence. He said those attending the breakfast largely understood.

He also said the breakfast was sold out before Sanders’ appearance was even announced. The Vermont independent is making a second run at the Democratic Party’s presidential nomination.

After it became clear Sanders wouldn’t be able to speak, Born said he arranged to have Sanders visit as a guest to meet and greet those going to the breakfast, but that plan also fell through with the campaign. Born said Sanders called him personally to apologize he couldn’t make it.

“A lot of us as individuals are big Bernie fans,” Born said. But he never intended Sanders’ appearance to be taken as an endorsement by the labor council, noting that the council does not endorse presidential candidates.

A spokeswoman for the Sanders’ campaign declined to comment Tuesday.

Despite Sanders’ absence, both Born and O’Brien said the crowd was pleased by the speech given by Jose La Luz, a veteran organizer who led the campaign to achieve collective bargaining rights for public workers in Puerto Rico. Since 2017, La Luz has been campaigning for Medicare for All.

“Jose La Luz really brought down the house, so I think everyone was pleased overall with the event,” O’Brien wrote in an email to the Portland Press Herald.