If by WS spec you mean JSR 109, then the answer is no. I'm not sure this is addressed by any specification - a missing header block that is not of interest to an endpoint is probably not going to be missed. However, if the endpoint expects and desires to process it and its missing, well that's a different matter. I would suggest sending a Sender SOAP Fault message back. Remember that intermediaries can remove headers. I guess this is a bit of a gray area.