Researchers conducted an experiment where they emailed a letter to 191 Congressional offices asking for a meeting regarding banning a chemical. They identified the writer either as a “campaign donor” or a “local constituent.” The researchers randomly assigned whether a Congressperson received a letter from a campaign donor or a constituent. (The researchers say they found volunteers who were actual campaign donors.)
Those identified as campaign donors were more likely to meet with senior staff or the Congressperson while the local constituents were more likely to meet with junior staff.
The reason for the different treatment remains unknown at this point to the researchers.