When Mick Mulvaney was named acting director of the Consumer Financial Protection Bureau in January, several critics expressed outrage over the appointment.

But only two went to court to try to block it.

The first was Leandra English, the deputy director, who was passed over for the top job when her boss, Richard Cordray, stepped down. And the second was the Lower East Side People’s Federal Credit Union, a nonprofit financial cooperative, whose modest size — just $54 million in assets — belies both its public profile and the scrappiness of its chief executive officer, Linda Levy. (Both legal actions were dismissed, and Mr. Mulvaney remains in place at the consumer bureau.)

This wasn’t the first time the credit union took on the establishment. Most notably, it acted as the bank for Occupy Wall Street, which sprang up in 2011 in protest over the financial crisis.

“People were donating money to Occupy Wall Street, and they had no idea where to put it,” Ms. Levy, 64, said. “So they opened an account here.”