IOWA CITY — The Iowa City Council has approved changes to the City Charter that increase the number of signatures required to force an initiative or referendum vote, but also allow for non-registered voters to sign such a petition.The council on Tuesday voted 6-0, with council member Terry Dickens absent, to approve amendments to the Iowa City Charter recommended by the Charter Review Commission - following several months of collaboration and debate by the city-appointed committee.“The Charter Review Commission put a lot of time into this,” said council member Michelle Payne.