“The leadership of the Democratic National Committee is now actively attempting to undermine our campaign,” Sanders campaign manager Jeff Weaver said at a press conference Friday afternoon. “This is unacceptable.”

The Washington Post first reported late Thursday that the Sanders camp acknowledged a low-level staffer viewed Clinton campaign voter data and was fired as a result. The DNC, in response, blocked Sanders campaign access to the party’s master list of likely Democratic voters until it provides a full explanation.