This question strikes a funny cord when you read it.  Generally employers ask how much information the can legally give rather than if they have to give it.  It makes one think that you have some sort of grudge against the employee and that you are acting maliciously in order to some way forestall him from being able to obtain a mortgage.  That would be a problem I would think.  If you intentionally tried to interfere with his obtaining a mortgage commitment by refusing to verify employment.  All you have to do is to verify dates of employment, salary and position.  Nothing more.  Do not give any reasons as to why the employee no longer works there.  It can lead to issues of defamation if they were fired for an unflattering reason.  Good luck.