After a complaint brought by Citizens for Responsibility and Ethics in Washington (CREW), the Federal Election Commission forced three Koch-backed groups to pay hundreds of thousands in fines and disclose millions in campaign spending.

Ever since the Supreme Court’s disastrous 2010 ruling in Citizens United v. Federal Election Commission, which allowed groups unaffiliated with campaigns to spend unlimited amounts of money on behalf of elections, there has been an enormous proliferation of “dark money” groups designed for exactly that purpose.

The poster children for these groups are Charles and David Koch, billionaires who bankroll numerous right-wing think tanks and advocacy groups through a network of shell corporations and “foundations.” The Koch brothers played a key role in funding the Tea Party protests, and have their hands in dozens of supposedly grassroots organizations opposing taxes, business regulation, healthcare reform, collective bargaining, gun control, and abortion rights.

In the Citizens United era, the FEC has largely been a toothless organization, with little manpower to enforce even the remaining campaign finance laws on the books — which is why their newest judgment against the Koch brothers is so significant.

During the 2014 midterms, the watchdog group Citizens for Responsibility and Ethics in Washington (CREW) filed criminal complaints against the Center to Protect Patient Rights (since renamed American Encore), a “secret bank” set up by the Koch brothers to funnel money to right-wing groups opposing the Affordable Care Act.

At issue in the CREW complaint was $2.3 million in undisclosed payments from CPPR to three right-wing advocacy groups in 2010: Americans for Job Security, the American Future Fund, and the 60 Plus Association. The groups argued that they did not have to disclose the money because it was for overhead rather than political advertising. The FEC disagreed, and last July levied a $233,000 fine.

While the American Future Fund and the 60 Plus Association disclosed their payments from CPPR months ago, Americans for Job Security had held back. But now they, too, have followed suit, disclosing a massive amount of previously-unreported campaign spending:

In a press release, CREW communications director Jordan Libowitz noted that, “This is what the fight for transparency is about,” adding, “Millions of dollars of political contributions that once were hidden are now exposed.”

“AJS showed a blatant disregard for campaign finance rules,” Libowitz continued. “These groups have a low bar to clear, but it appears it is still too high for some of them.”

And this was not the first time CPPR was found illegally covering up political spending: A state case brought against them in 2013 by then-California Attorney General Kamala Harris resulted in a $1 million judgment and the return of $15 million in illegal donations.

However, as noted in their press release, the CREW complaint led to the largest federal fine for campaign finance violations in U.S. history. And the Koch brothers’ problems may not be over — CREW has also filed complaints with the IRS and the FBI, alleging CPPR lied on its tax returns.

Despite every attempt by Republicans and the Supreme Court to eviscerate regulation of campaign finance, the victory of CREW proves that there is still recourse to hold right-wing billionaires and their shadowy political networks accountable.