Oregon Live has a story about current efforts by the Oregon Department of Agriculture to regulate wild birdseed. The ODA wants the authority over the content of wild birdseed, to address the contamination of the seed by agricultural weeds and invasive plants. The state's House Agriculture and Natural Resources Committee will take up the issue this Tuesday. According to this brief note at the Capital Press, they are also expected to consider a related bill that would require wildflower seed packaging to be labeled with information including the presence of noxious weeds.
Earlier this month, the general issue of birdseed contaminants came up on the ma-eppc listserve, you can read the comments here (the top one is from me).