The Democratic Senatorial Campaign Committee has asked to the Federal Election Commission to investigate political activity by three conservative advocacy organizations expected to spend millions of dollars on the 2012 election, Bloomberg reports.

The complaint, filed Monday, targets Republican operative Karl Rove’s Crossroads GPS; Americans for Prosperity, a group associated with billionaire donors Charles and David Koch; and 60-Plus Association, which has ties to Carl Forti, Crossroads’ political director.

“These organizations are actually claiming that they are no more political than a church, a synagogue, or even the American Cancer Society,” Guy Cecil, executive director of the campaign committee, wrote to commission. “It is patently absurd and we certainly expect that the FEC would take action.”

The complaint is the latest in a series by Democrats and watchdog groups against such 501(c)(4) nonprofits, which are not required to reveal their donors. Senate Republicans have blocked efforts to mandate such disclosure.