The Chicks have been "forced to postpone" three more shows on their national tour amid doctor's orders for vocal rest. The news comes after the band left the stage in Indianapolis on Sunday after just 30 minutes.MORE: Gavin Rossdale pays emotional tribute to Foo Fighters drummer Taylor Hawkins after his untimely deathIn a statement they apologized to fans, writing: "Indianapolis, we are so sorry we could not give you the show you deserved OR the show we wanted to give you.