Here's a unique thought....Review your contract.
Additionally the auditor may be acting upon his own organization requirements and its understanding of the application of ISO 17021 requirements.
What's the big deal anyway? Is there something not happening on the other shifts the auditor shouldn't see? If you "maintain" your system effectively all aspects of it should be able to demonstrate conformance at any time, not just at "Audit" time or at your convienence.
The audit has to be a representative sample of the whole....just looking at the day shift doesn't meet that.
While ISO 9001 does not require auditing all shifts, I always encouraged my clients to do so. Follow this reasoning:
Where do you put new employees --- third shift.
Where are your most inexperienced people --- third shift.
Where do you find most of your off quality or problems --- third shift.
Then why are you not auditing all shifts??
Try writing a requirement agaist a best practice regarding ISO 9001 and watch the client, and rightfully so, call the auditor on an non existing and clear requirement.
Now there is a requirement imposed by the IAF, pushed down to the AB's and then the CB's and subsequently the audtiee.
You know what rolls down hill, don't you?
Then there is IAF (International Accreditaion Forum of which ANAB is a member) MD 5 Section 3.5
"Where product or service realization processes operate on a shift basis, the extent of auditing of each shift
by the CAB depends on the processes done on each shift, and the level of control of each shift that
is demonstrated by the client. The justification for not auditing each shift shall be documented."
If your CB issues an accredited certificate by an AB that is a member of the IAF, then this DOES APPLY. Again, ANAB HAS stated what they will and will not accept.
Check with your Registrar (CB - Certification Body). If anyone doubts my response, look at the IAF website and look for the MD's. It's not a matter of the auditor interpretating the CB's requirement. It is the CB pushing down the actual requirement from above.