Citizens for Responsibility and Ethics (CREW), a Washington government watchdog group, filed complaints against 10 so-called dark money groups this week, alleging that the nonprofit organizations have been “significantly underreporting their political activity.” The groups, which can opt to not disclose their donors, are limited in the percentage of their expenditures that can be spent for overt political purposes.

The list includes organizations that have spent hundreds of thousands of dollars on political advertising or have donated to super PACs supporting mostly conservative candidates across the country. CREW filed criminal complaints with the Department of Justice concerning six of those groups, asking that the FBI and the Justice Department investigate whether the groups’ IRS tax filings misrepresented the amount of money spent on political activity.

Among those on the list are several organizations that spent money on advertising in the Republican primary for the Arizona governorship, in support of now-Sen. Ben Sasse in his Nebraska Republican Senate primary race and in favor of then-Speaker John Boehner in his Ohio re-election bid.

“The disastrous Citizens United decision opened up the floodgates for dark money groups to spend on politics,” Noah Bookbinder, executive director of CREW, said in a statement, citing a case between the conservative nonprofit and the Federal Election Commission. “But there are still some limits to the amount of spending and secrecy these groups are permitted — and too many brazenly ignore these modest limits.”

Political nonprofits like the ones named in the CREW complaints have heavily ramped up their political spending since the 2010 Citizens United decision, which relaxed campaign finance rules and gave corporations and some nonprofits the green light to spend cash on distinctly political ads. In each political cycle up until the 2008 election, dark money groups spent less than $1 million, collectively, on political ads. In 2008 that amount jumped to $10.2 million, according to Center for Responsive Politics data. So far in 2016, dark money groups have spent $36.9 million, already breaking the previous record set in 2014 ($30.9 million), according to the CRP.

The nonprofits, usually classified as 501(c)(4)s, are legally required to focus the majority of their funding on “social welfare” issues to maintain their nonprofit status.

The dark money groups named in the CREW complaints are the American Dream Initiative, the Arizona Future Fund, Freedom Vote, the Jobs and Progress Fund, the Legacy Foundation Action Fund, Michigan Citizens for Fiscal Responsibility, the Mid America Fund, Moving Ohio Forward, Oklahomans for a Conservative Future and the Rule of Law Project.