In Illinois, House Bill 723 would make it so that, according to the article on Green Party Watch (since I can’t figure out how to put it in my own words), “when no candidate of an established party runs in a primary for a particular office, that party can only fill the vacancy in nomination if the candidate they “slate” collects a large number of signatures.” The bill has obtained the distaste of the Green Party.
The sponsor of the bill would have been uncontested in 2008, if the Green Party didn’t slate a candidate. The same thing goes for the co-sponsors.
You can read the full article here. Source: Green Party Watch.