Opponents of Oregon’s Measure 90, the top-two system initiative, have established this web page.
This newspaper story says that former New York city Mayor Michael Bloomberg will probably contribute a substantial sum of money to assist the campaign in favor of the top-two system. The story mentions that Bloomberg’s emissary to Oregon for this purpose was Bradley Tusk. Tusk formerly worked for U.S. Senator Charles Schumer, who had an op-ed praising top-two systems in the New York Times last month.
Blue Oregon has this commentary on Measure 90, by Carla Hanson. Thanks to Blair Bobier for the link to the story about Mayor Bloomberg.