A new study offers the first scientific proof that members of Congress and top staffers are more amenable to meeting with an identified campaign donor as opposed to one who identifies as a regular constituent.

Working with the liberal grassroots activist organization CREDO, graduate students Joshua Kalla, of Yale University, and David Broockman, of the University of California-Berkeley, conducted the study by sending meeting-request letters to 191 members of Congress.

At random, recipients were sent letters identifying the citizen as either a prospective “donor” or a “constituent.” The letters were identical in all other aspects, and no other information about the individual was provided.

The researchers found that letters from “donors” were much more likely to receive favorable responses for meetings with the Congress member or a top staffer. Letters from “constituents” were more likely to ignored or passed on to a lower-level staff member.

"Here we have a case where [there are] people separate from the member of Congress who may or may not have donated to the member of Congress," researcher Kalla told The Huffington Post. "All the member of Congress knows is that they're donors. These people are granted special access. So that really flies in the face of the ruling and the reasoning behind Citizens United."

The 2010 Citizens United Supreme Court decision created a new level of ease for lush for funneling campaign contributions to candidates through outside groups. The Court insisted at the time that there was no correlation between money and access to politicians.

"Independent expenditures do not lead to, or create the appearance of, quid pro quo corruption,” wrote Justice Anthony Kennedy in the majority opinion. “In fact, there is only scant evidence that independent expenditures even ingratiate."

The study was embedded in CREDO’s unrelated lobbying efforts last summer to push a bill that aimed to ban a chemical. CREDO sent the letters to unwitting congressional offices from actual donors and constituents with all intention of following up with any scheduled meetings, the researchers wrote.

"We were dismayed to see the Supreme Court decision in the Citizens United case, and particularly the fact that it was based in part on the fact that they suggested there was no evidence that there was any corrupting evidence of federal campaign donations on the political process,” said CREDO Political Director Becky Bond.

“So this study is so exciting because it's the first scientifically based evidence that we've seen that there is a real link between campaign donations and federal policy.”

Bond told Huffington Post that CREDO often works with political scientists and others on studies "largely aimed at, how do we help average citizens have a greater impact on democratic processes?"