I have had the same request, and the underwriter requesting this is no "fly by night" company, but one of the largest underwriters in the country.  Also, it is absolutely untrue that the client can't file an E&O claim against you....happened to me. As my attorney said, it is unethical but not illegal.  It's a huge surprise when that letter comes in the mail!  I have asked the underwriter to give me the reasoning on this, and am waiting for an answer.  My question now is, what's the big deal?  If they have your dec page, or certificate of insurance, then they have all the information they need to contact your E&O carrier.  There's not much else in the policy that they shouldn't see.