RoseAnn DeMoro stood in front of 300 nurses in an auditorium in Oakland, Calif. on Tuesday afternoon, while 11,500 more nurses listened on the phone. Two of their own had just contracted Ebola, and she was furious.

“We’ve been lied to in terms of the preparation in the hospitals,” she declared. “We’ve been essentially ignored by the White House and the CDC, and they’ve been giving the hospitals far too much credit in assuming that they would actually be taking their advice.”

DeMoro’s union — the 185,000-member National Nurses United — has for weeks been decrying the lack of protective measures at the Dallas hospital where an Ebola patient had been treated. Then, while other groups issued mild statements or nothing at all, they sent a letter to President Obama, Congress, federal agencies and state governors demanding more protections for health-care personnel. “If the nurses controlled the resources, there wouldn’t be an Ebola crisis in this country,” she roared to her fellow nurses, singling out declining emergency preparedness budgets.

This is business as usual for National Nurses United. It’s one of the nation’s youngest unions, but it’s also one of its most aggressive, on subjects that more traditional unions won’t touch — and it’s been making more headlines than labor groups many times its age. It does opposition research on political candidates, it uses fiery language and weighs in on topics that seem far afield from nursing, such as fossil fuels and bank taxes.

It is not an approach that all other unions agree with, and not one that makes all nurses, known for being anything but combative, comfortable.

Some other unions “roll their eyes when they hear at the NNU,” said Patricia Pittman, an associate professor in the department of health policy at George Washington University, who has studied the health-care workforce.  “They don’t view them as representing their kind of nursing” — which might involve a more genteel, bedside manner sensibility.

The group’s roots go back to 1995, when the California Nursing Association — then led by DeMoro, a former Teamsters organizer from St. Louis — broke off from the American Nursing Association, desiring a more aggressive approach to pressuring hospital owners for better wages and benefits.

But eventually, other state nursing associations later broke off, too, and they all united in a mega-union called the National Nurses United (NNU) in 2009. The goal, they say, was to push harder for rank-and-file nurses when demands on them were increasing as the healthcare industry has grown and changed — mounting staff shortages coupled with high turnover, sicker patients, and increased use of ever-changing technology. It’s since launched some of the largest strikes and walkouts in the profession’s history, which other nursing unions have tended to be more genteel.

“Direct care staff nurses began to feel that the professional associations were not representing their interests. That led to a split in the nursing community,” says Pittman. “It’s very much ‘roll up your sleeves, put up your fists, and don’t mess with me.’ They’re tapping into a lot of rage for working conditions for nurses.”

NNU is the largest nursing union in the country, with about 185,000 members, and the only one that’s exclusively nurses. The others are divisions of groups like the American Federation of Teachers and the Service Employees International Union, which primarily represent other sectors. NNU has fought bitterly with other unions for members, sometimes blocking their attempts to sign nurses up in order to add them to its own rolls instead. It buried the hatchet with the SEIU in 2009 after a long rivalry, only to start beefing again three years later.

The biggest difference between NNU and other unions, though, isn’t the group’s combative approach.  Rather, it’s the targets the group takes on.

Sure, they’ve done the nuts and bolts of collective bargaining, like negotiating over wages and working hours and nurse-to-patient ratios. But they’ve also staffed health stations at Occupy Wall Street camps, backed a “Robin Hood Tax” on financial transactions to fund social goods, marched against the use of fossil fuels, protested water shutoffs in Detroit, and emerged as a strident voice for a single-payer health-care system. It’s also played hard in politics, taking on Meg Whitman in her race for California governor against Jerry Brown. Indeed, the story of the undocumented maid who helped undermined Whitman’s candidacy was planted by NNU, the San Francisco Chronicle reported.

The activism is explained by the union’s view as a defender of public health and social justice, says Deborah Burger, one of the union’s co-presidents.

“The reason we formed NNU was that there was a huge vacuum in nurses unions that would be willing to take controversial stands on a number of issues, and we felt that it was much better to have one voice on social issues,” Burger says in an interview. “For decades, we’ve been working to get the nurse not only to advocate for their patients in the hospital, but actually for patients and the community.”

This week, though, their first concern is that front-line nurses could be exposed to Ebola.

On Tuesday’s call, nurses from all over the country described their fears about going to work at hospitals without state-of-the-art protections. After NNU described how it had sent 1,000 hazmat suits to Liberia, one nurse on the line called Ebola the “nurse-killer disease.”

“My God,” said DeMoro, after many had had their chances to speak. “My God, I think that sent a chill through everybody on this call.”

She went on, warming to her soapbox, touching on the themes of systemic injustice that have run through the rest of her activism.

“I think a lot of nurses are mad at the CDC. But this goes much further than the CDC,” DeMoro said, building to a crescendo. “This is a bipartisan lack of political will, and now those roosters are coming home to roost. Even the rich people who fight against a public health system could be exposed.”

Despite her sense of moral rectitude, though, DeMoro seemed to realize that NNU is out in front of even those other advocates that might call themselves allies in the cause of protecting public health.

“The NNU is not going away. We’re not going to be delegitimized, we’re not going to be silenced,” DeMoro finished, now talking to the hundreds of Bay Area nurses assembled in front of her. “You’ve got the people of the world with you. When people say, you’ve got all these groups agreeing with the CDC, who’s on your side? We say ‘oh that one small group, it’s called the public.’”

There was long, loud applause.