Nonprofit workers, centered in the District but also in states such as California, Maryland, Alabama, and New York, have helped swell the NPEU’s ranks 30 percent over the past year.
The federal government does not track union representation among the more than 12 million nonprofit workers.
Magnets for younger, highly educated and idealistic workers, nonprofit groups have long been known for a culture of unpaid hours, low salaries and thin budgets.
“CBPP is committed to making the organization the best it can be,” the nonprofit group’s president, Robert Greenstein, said in a statement.
In November, the union filed an unfair-labor complaint against an advocacy group for transgender rights, the National Center for Transgender Equality.