ICLEI is not a treaty.
ICLEI does not cede any sovereignty in any way, shape, or form.
Half of the ridiculousness of Mr. Maes' paranoid fantasy is that he doesn't even understand what ICLEI is.
http://www.iclei.org/
"ICLEI provides technical consulting, training, and information services to build capacity, share knowledge, and support local government in the implementation of sustainable development at the local level. Our basic premise is that locally designed initiatives can provide an effective and cost-efficient way to achieve local, national, and global sustainability objectives."