Sanders drew a distinction between National Nurses United For Patient Protection, a super PAC that has spent at least $569,000 backing him, and those super PACs backing other candidates during an interview with CNN's Brooke Baldwin.
"What I have said over and over again is that I have not and will not raise a nickel for a super PAC," Sanders said. "I am the only Democratic candidate who does not have a super PAC. I will not have a super PAC. They are nurses and they are fighting for the health care of their people. They are doing what they think is appropriate. I do not have a super PAC."
Sanders is correct that he has not raised money for the nurses super PAC, which is affiliated with National Nurses United, the first national union that backed his campaign. But in past statements, Sanders and his campaign aides have gone farther than saying the Vermont senator simply would not raise money or coordinate for a PAC. They have also said he would not take a super PACs help.
"We stand by our position that we do not want the help of a super PAC," Jeff Weaver, Sanders' campaign manager, said earlier this month after CNN wrote a story
on the union super PAC supporting Sanders.
Campaign aides would not say whether that meant the campaign would ask the super PAC to stop its spending. While the campaign is not able to tell the group what to do, a public statement disavowing the super PAC would send the pro-Sanders group a clear signal.
Sanders is by far the most outspoken anti-super PAC candidate running for president in 2016. Nearly every speech he gives mentions that the influence of super PACs and reiterates his pledge to not associate with them. Many of his supporters grow animated when asked about Sanders' anti-super PAC position.
"I don't have a super PAC," he told reporters in Washington over the summer. "I am not going to have a super PAC."
"I made a decision -- now it wasn't an easy decision -- I said if I am going to walk the walk and not just talk the talk, I am not going to have a super PAC," Sanders told NPR in November.
He has also knocked Hillary Clinton, the Democratic frontrunner, for embracing super PAC money.
"Now, I have many disagreements with Hillary Clinton. And one of them is that I don't think it's good enough just to talk the talk on campaign finance reform. You've got to walk the walk," he said earlier this month at an MSNBC campaign forum.
This rhetoric, however, does not square with the group now spending on his behalf and offers proof that it will be difficult for Sanders to stick to a no-super PAC pledge.
A bulk of the group's spending -- which is funded by union members -- has been on printing pro-Sanders literature and online and print advertising.
Michael Lighty, the nurses union political director, argued earlier this month that the group was not a super PAC.
"This is not a super PAC," he said. "It is really a different animal."
But according to the Federal Election Commission, that isn't the case. An FEC spokesman told CNN on Wednesday that National Nurses United For Patient Protection is, in fact, a super PAC, despite being established in 2009, before the 2010 U.S. Supreme Court decision that led to the proliferation of super PACs.
National Nurses United super PAC is different than those supporting other candidates, like Priorities USA, a PAC backing Hillary Clinton, and Right to Rise, a group backing Jeb Bush. Both of those organizations have raised millions of dollars with the blessing of their respective candidates and are generally run by former aides.
After CNN's story, Deborah Burger, co-president of National Nurses United, said that the super PAC was "proud to support Bernie Sanders and will continue to do so."