Clinton will slightly increase her delegate lead over Sanders.
Wisconsin Democrats passed a resolution encouraging a change or end to the superdelegate system.
The local party president called the allegations "preposterous."
Sanders told the media not to count him out after Tuesday.
A campaign aide said Sanders officials were initially denied certifications to organize imprisoned voters.
Clinton has 49 percent support to Sanders's 47 percent.
A majority of Democratic voters want Bernie Sanders to stay in the primary.
Tuesday is the deadline for primary campaign donations.
Sanders is campaigning ahead of the state's June 7 primary.
Sanders now has 43 superdelegates supporting him.