Do customers with a business account titled for example: John Doe DBA Construct All Construction, need a NAICS code? We have quite a few "Doing Business As" accounts and all are of course sole proprietorships having other personal accounts under the same CIF. I get mixed opinions on whether NAICS codes are needed.

You would assign an NAICS code that relates to the type of business conducted, in this case construction. NAICS has nothing to do with form of ownership; they are used by the government to classify business types (census bureau) - that is the genesis of these codes, and among other uses by banks to track lending concentrations, by D&B to classify similar businesses, and most recently to classify deposit account customers for BSA industry classifications.

For the NAICS codes to serve their purpose, you just assign one every time you open a non consumer account. There are no issues of personal judgment as to when you do or do not.