A powerful activist investor group called for Mark Zuckerberg to step down in a statement today, citing new admissions of irresponsibility in the CEO’s planned testimony to the House Energy and Commerce Committee.

“Mark Zuckerberg’s prepared testimony highlights a simple fact: He doesn’t understand how a large, global and publicly-held company is run,” Open MIC CEO Michael Connor said in a statement. “He currently has two jobs at Facebook — CEO and Chairman of the Board. It’s time for him to give up at least one, if not both, titles.”

“It is long past time for Facebook to separate the roles of company CEO and Chairman,” Connor continued, “and for Mark Zuckerberg to resign or be fired.”

While Open MIC does not hold any Facebook shares, it has a history of coordinating Facebook investors to call for more responsible behavior from the company. Earlier this year, the group coordinated requests for a shareholder report on election interference and other platform challenges, as well as a separate request to establish an ongoing risk oversight committee.

Open MIC isn’t the only group bringing pressure on Zuckerberg. Last week, New York City comptroller Scott Stringer called for similar changes in Facebook’s board structure on behalf of the city’s municipal pension fund, a significant investor in Facebook. Stringer cited recent declines in the company stock as a result of seemingly irresponsible behavior. The company’s stock has declined nearly 15 percent since the most recent Cambridge Analytica details came to light. “We think there needs to be more board oversight,” Stringer said. “We think there needs to be an independent chairman of the board.”

Over the weekend, a separate editorial in The San Francisco Chronicle also called on Zuckerberg to resign.

The Facebook founder has adamantly resisted any calls to give up control of the company, telling The Atlantic in an interview this morning that he had not considered resigning because he’s “very confident that we’re gonna be able to work through these issues.”

Zuckerberg holds only 16 percent of Facebook stock but retains 60 percent of the company’s voting rights, making it all but impossible for investors to unseat him against his will. In September, Facebook’s board blocked a plan that would have entrenched Zuckerberg’s voting power even further by reclassifying the company’s stock.

Still, the calls for restructuring will likely increase the pressure on Zuckerberg as he prepares to testify before Congress later this week.