A labor union’s strength is implied in its name: unity. There’s a reason Marx and Engels called on the workers of the world to “unite,” not “get together and agree, sort of.” Unions fall apart when their members stop working toward the same goal.

This Democratic primary has tested that idea. While Hillary Clinton quickly secured endorsements from a slew of large labor organizations in 2015, more than a dozen local and regional union groups have broken with their national leadership and voted to support Bernie Sanders instead. While it’s common for a national union to stay neutral so its regional affiliates can endorse independently, it’s far more rare to see a local affiliate buck the will of its leadership and tack in another direction. That’s exactly what’s been happening.

Some people might think of unions solely as large, national organizations, like the United Auto Workers. But behind every national labor organization is a web of “locals,” the far smaller affiliates who often represent workers at a handful of job sites, be it a factory, a hospital, or a newsroom. Many of the Clinton endorsements were decided by national executive boards, which are often small groups of professionals based in Washington, D.C. Sanders has largely won his support among locals, as well as at regional committees.

Take the Washington Federation of State Employees, which represents 19,000 people. Although its parent union, the powerful American Federation of State, County, and Municipal Employees, endorsed Clinton in October, the state council thought differently. In January, its executive committee voted to support Sanders and suggested their national leaders take another look at the endorsement process.

“Maybe we need to blow this up,” WFSE public affairs director Tim Welch said. “Yes, we’re a representative democracy here [in the union]—but what if we had all the members directly select who they’d like to recommend? This is an opportunity to rethink how we do endorsements.”

Such talk was not common a year ago. Surveying the presidential race last July, unions looked right and saw a Republican field filled with the likes of Scott Walker, then looked left and saw Clinton flanked by a bunch of random men. Though the American Federation of Teachers was the first major union to endorse Clinton, it was joined within months by heavyweights like the Service Employees International Union and the United Food and Commercial Workers, which represent about 2 million workers each.

This was great for Clinton. An endorsement from SEIU? That’s something every Democrat wants, nearly as badly as Republicans want an “A” rating from the National Rifle Association. What’s more, several of these major labor unions supported Barack Obama during the 2008 primary, lending credibility to Clinton.

The notable exception, however, was the Communication Workers of America. At 700,000 members, it is a sizeable union that primarily represents telecommunications employees. Last December, after a general membership vote, it endorsed Sanders.

That CWA vote marked a break in how things are done. As the Sanders campaign heated up, this led to some hard feelings in other unions. After the American Federation of Government Employees executive board voted to endorse Hillary Clinton in December, an irate worker wrote an angry column in response, titled “Why Did My Union Give an Early Endorsement to Hillary Clinton Over Bernie Sanders?”

Within the first hours of the AFGE's release, the union’s Facebook page was filled with statements in support of Sanders. Within days of the news, the Facebook page “AFGE for Bernie” nearly tripled its membership … Why did AFGE's leadership feel this urgency to endorse so quickly after so many members made it clear they wanted to endorse Sanders or wait to endorse?

That question has preoccupied Larry Cohen. The energetic former president of the CWA is now stumping for Sanders; he spoke with me from a train after joining the senator at a rally with striking Verizon workers. He knows firsthand how many unions make their endorsements from the top down, with limited member involvement, and how much that’s angered people. It means he occasionally has to step lightly.

“I’m careful in those situations,” he said. “I see my role as mobilizing active members, not actually creating internal divisions. If I’m appealing to a local, it’s going to be one where the national union hasn't endorsed anyone.”

That said, he won’t turn away any support. Since the Sanders campaign largely relies on volunteers for labor outreach, Cohen is more interested in drawing new, individual supporters than bringing entire locals over to Bernie. But even when a regional affiliate does endorse Sanders against the wishes of its national leadership, he says he hasn’t caught much flack. “Nobody has called me about anything I've done. I've had no complaints from those organizations,” he said.

And so the Sanders surge among union locals continues. In Pennsylvania, which holds its primary on April 26th, an AFT-affiliated association of community-college instructors and staff recently considered endorsing the Vermont senator. They’ll hold off for now, said John Braxton, the local’s treasurer: While Sanders prevailed in a poll of local membership, he didn’t clear the preset bar of 60 percent to trigger the announcement. Braxton said his local’s decision may have prompted some quizzical looks from union leadership, but no backlash. “I don't think we're going to have heavy repercussions from this. It’s kind of a dispute within the family,” he said. “And we're going to be a family when it’s over.”

That’s something I heard from every union member I spoke with: This temporary split will not affect overall unity. Without a doubt, most labor organizations will align behind the Democratic nominee once this primary shakes out; there’s little appetite for a President Trump or Cruz.

Still, the back-and-forth over endorsements suggests a deeper issue among unions. If the labor movement’s strength is unity, its weakness is a reflexive worship of hierarchy: Locals supply the labor, and the national leadership sets the direction. That’s the way it has been for years, but it may be changing. Locals have signaled they want a bigger say in national political decisions. Until they get it in a meaningful way, divided unity will continue.