Some supporters have taken steps to create super PACs, only to abandon their efforts after realizing it wouldn’t sit well with the campaign. Others have forged ahead with spending operations that qualify as super PACs, while defiantly rejecting the label.

Take National Nurses United, the largest nurses’ union in the U.S. The group endorsed Sanders for president back in August. Its political arm—National Nurses United for Patient Protection—has so far spent more than $550,000 in support of Bernie Sanders, including doling out money for print and digital advertising. The group qualifies as a super PAC, according to the Federal Election Commission. Union organizers, however, reject that name.

“It’s not a super PAC, super PACs are corrupt,” RoseAnn DeMoro, the executive director of National Nurses United, said. “They’re a way for the billionaires to influence the political process and spend unlimited money. This is nurses who want to get our support for Bernie out there. That’s way different than the Koch brothers. This isn’t big money. I think people understand the difference.”

That denial points to a disconnect between public perception of what a super PAC is and how they operate on the ground. Voters often associate super PACs with billionaires and vast sums of corporate money. But not all are alike. The groups can also raise unlimited amounts of money from individuals and labor unions.

“There’s always more nuance to these things when you get away from strict legal definitions and out into the real world,” said Larry Noble, the general counsel for the Campaign Legal Center and former general counsel for the Federal Election Commission. “If you want to look at a report and simply count up the number of super PACs supporting a candidate, that wouldn’t give you a true picture of what’s actually happening.”

On Thursday, Sanders won the support of Communications Workers of America, another major labor union. At an event announcing the endorsement, a similar tension was on display. Sanders denounced big money in politics, but CWA president Chris Shelton indicated the union is likely to use its super PAC to support his campaign. “We will respect Bernie’s wishes, but we will use all legal and possible resources to get him elected,” Candice Johnson, a spokesperson for the union said. “We do have a super PAC, but it’s a super PAC of a union of 700,000 working people, not a couple of billionaires. That’s a big difference.”

Sanders, for his part, has forcefully and repeatedly insisted that he does not have—or want—a super PAC. His campaign has been explicit as well. Earlier this month, after the Associated Press reported that an Oakland-based progressive super PAC plans to spend money in support of Sanders, the campaign emailed supporters with the message: “we don’t want this super PAC’s help.” The campaign has also sent a cease and desist letter to another pro-Sanders super PAC, alleging a violation of federal law.