Not all dark money is the same. Unlike corporations and individuals, organized labor is forced to play by a different set of rules.

In the very dark election of 2014, voters still have no clue about who paid for a significant portion of the election efforts propping up a whole new Congress. Many donors hid behind 501c non-profit shells to conceal their identity, while spending millions of dollars to influence the outcome through advertising and get-out-the-vote programs.

We may never know the names of the men, women, and corporations that funded the 2014 election. However, we do know some of the unions.

Many unions face extensive disclosure requirements, forcing them to disclose detailed spending records to the Department of Labor. Starting in the 1950s, extensive reforms on union activity required that organized labor submit financial records to government regulators. Those records, reviewed by Republic Report, reveal the money trail behind many of the leading dark money groups in the election this year.

Patriot Majority USA, the largest dark money group supporting Democratic candidates this year, focusing on competitive Senate elections, was the main beneficiary of union money. The National Education Association, which represents teachers, gave the group $100,000. The Teachers and Firefighters of the AFL-CIO also gave $100,000 each. State County & Municipal Employees of the AFL-CIO gave $16,250, bringing the total union contributions disclosed in the Labor Department record system to Patriot Majority to $316,250.

At least one pro-Republican dark money group also benefitted from labor union money. The Laborers National Headquarters and the International Union of Operating Engineers gave four contributions to the U.S. Chamber of Commerce during this campaign cycle, with a combined amount of $150,000.

VoteVets.org Action Fund, another pro-Democratic dark money group, received $100,000 from the American Federation of Government Employees.

The imbalance of disclosure requirements give corporations and wealthy individuals greater secrecy in elections than organized labor. A quick fix to all of these problems would be to require groups that air independent expenditures as well as issue-based political advertisements to disclose their donors, regardless of the donor or group type. In the last Congress, a minority of Senate Republicans filibustered such disclosure reforms. It appears that a new Senate Republican majority in the next Congress is even less likely to adopt such a solution.