It had all the trappings of a re-election rally: thousands packing a convention center, Barack Obama T-shirts, videos celebrating the health care law, and a wall-size banner with encouraging messages to the incumbent president.

“You are our knight in shining armor — Sarah C., Norman, Okla.,” read one inscription.

But this Obama love fest in Washington was not a campaign event. The nearly 9,000 gathered were teachers in town for the National Education Association’s weeklong annual convention.

For the Republican teachers in attendance, the digs at their political views were impossible to overlook.

“What I don’t like is the harassment going on for people to be an `EFO’ — an educator for Obama,” said Maureen van Wagner, a special education teacher from Anchorage, Alaska.

In interviews with The Associated Press, roughly a dozen teachers who identified themselves as Republicans said they felt pressure from union leaders and the rank-and-file to support Obama’s re-election — and felt marginalized when they wouldn’t. Some interviewed said they were so worried about retribution from their colleagues that they wouldn’t provide their names for publication.

National unions such as the NEA — it’s the largest teachers union in the U.S. — have long been stalwart supporters of Democratic candidates, and to be effective, they must speak with a unified voice. But teachers, like other professional groups, are not monolithic in their political views, prompting inevitable tensions when the union mobilizes its political machine.

NEA leaders have been urging members to hold house parties to educate their friends about why Obama, who addressed the convention Thursday by telephone to thank teachers for their support, deserves a second term. So it wasn’t really a surprise that the union showed its support for Obama so overtly at the convention. After all, 72 percent of delegates at last year’s NEA convention voted to endorse Obama for re-election — the earliest the group has ever endorsed in a presidential election cycle.

But what did take Republican teachers off guard was the criticism they received for expressing support for Mitt Romney.

A Republican teacher speaking at the convention was booed for doing just that. The incident prompted NEA President Dennis Van Roekel to intervene, saying that everyone had the right to speak. And when the union invited delegates to the Democratic National Convention in September to a special meeting, no such invitations went out to delegates to the GOP convention until a Republican teacher complained to Van Roekel — an error the union said resulted from a missed newsletter deadline.

Then there were the T-shirts. Some Republicans said they were presented with NEA T-shirts featuring Obama’s name — and that it felt like being forced to choose between their profession and their politics.

“I’m not here representing myself, I’m here representing other teachers,” said Chris Cvijetic, a first-grade teacher and Republican from Palm Springs, Calif. “That’s the only way I can get through the day.”

NEA officials said the union, which has never endorsed a Republican for president, makes every effort to ensure all its members feel welcome. The union holds a Republican Leadership Conference the same week as the annual convention. Union dues are kept separate from the NEA’s political action committee, which spends donated funds to promote candidates such as Obama. And the NEA has endorsed GOP candidates who are pro-public education.

Despite the complaints, the NEA has no plans to shy away from a full embrace of what Mary Kusler, the union’s director of government relations, called “the incredible legacy and vision of this current administration.”

That’s not stopping NEA members who disagree with Obama from making their voices heard.

In the convention center’s basement-level expo center, squeezed in between the gay, lesbian, bisexual and transgender teacher’s caucus and a stall selling designer handbags of questionable authenticity, sat a small, two-person table for the NEA’s Republican Educators Caucus. The group has about 160 members, although it has seen its ranks grow in recent years, said Davina Keiser, the caucus chairwoman.

“For Republican teachers, it’s almost like we’re stepchildren in NEA, and then in the Republican Party we’re also stepchildren, because we’re public schoolteachers, and that’s not part of their focus,” said Keiser, who teaches high school math in Long Beach, Calif.