A tech billionaire's six-figure contribution to a political nonprofit and a legally murky attempt to reclassify the donation have created an uncomfortable situation for progressives in Colorado, where the incoming Democratic secretary of state made reining in unaccountable "dark money" spending a central tenet of her campaign.

A series of campaign finance complaints, first reported by Complete Colorado , allege that the charitable foundation of Google co-founder Sergey Brin contributed $170,000 to a nonprofit progressive issue committee called ProgressNow that was fighting an effort to increase the amount of Colorado land available for oil and gas drilling.

Charles Heatherly, the former policy director for the Colorado state Senate Republicans, wrote in the complaint that the contribution was funnelled to another group called Colorado Rising to distance the Sergey Brin Family Foundation from spending on the ballot issue. He argued that the intermediary nonprofit organization, ProgressNow Colorado, should be registered as a political issue committee and have to disclose donors and comply with spending rules.

The complaint involving two of the state's most prominent progressive groups and a powerful tech billionaire is emerging as one of the first major challenges for Democratic Secretary of State Jenna Griswold, who ran a campaign partly on getting so-called "dark money" out of the political process. Conservatives have long accused tech companies, Google among them, of harboring a bias toward conservatives. Heatherly has asked that Griswold "recuse herself and retain an independent investigator to look into the matter."

The issue highlights the tension that some liberal politicians across the nation face in trying to rein in unaccountable political spending as it becomes more ubiquitous in campaigns. In their first bill since retaking a majority, House Democrats in Washington targeted dark money with provisions that would force certain politically active "social welfare groups" to disclose major donors. The legislation is likely dead on arrival in the Republican-controlled Senate.

The effort comes on the heels of an election cycle where Democrats were the largest beneficiaries of dark money spending, according a recent analysis of campaign finance data from the Center for Responsive Politics by Issue One. The analysis found that 54 percent of the approximately $150 million spent by these groups favored Democrats, a sharp reversal of recent cycles.