Courts can never waive subject matter jurisdiction. Even if a case is already underway, if it is determined that the court does not have subject matter jurisdiction, the case is thrown out. For example, in the case of Belleville Catering v. Champaign Market Place L.L.C. (350 F.3d 691 (7th Cir. 2003), Belleville sued in Federal Court based on diversity of jurisdiction. The case made it all the way to the
appellate level before anyone noticed that in their filing Belleville listed their State of Incorporation wrong. They were from the same State as Champaign! Therefore there was no diversity and the case was thrown out.