No presidential candidate fighting for their party’s nomination has ever benefited from as much undisclosed cash, and watchdogs worry the pro-Rubio group’s unchecked activity serves as a dangerous precedent that will soon become common practice.

“It is now the model for a how a candidate can inject unlimited, secret, corrupting money into their campaigns to benefit their election,” said Fred Wertheimer, president of Democracy 21, a campaign watchdog group. “That is precisely the kind of model that we do not need in America.”

The pro-Rubio nonprofit, known as the Conservative Solutions Project, was created in early 2014 and run by some of the same political operatives who would later lead for his super PAC, including South Carolina strategist Warren Tompkins. Both groups can accept unlimited donations from donors, but unlike like the super PAC, the nonprofit can keep its contributors hidden from the public — permanently.

The Conservative Solutions Project operates under the “social welfare” 501(c)4 section of the tax code, which requires such groups not be primarily involved in political matters.