Are NAICS codes unique by employer?

I know employers can have more than one NAICS code based on the range of activities they engage in. I am curious as to how possible it is that employees of the same company are assigning themselves different industries, or if there is some unique assignment.

As per this NAICS FAQ, while some agencies may assign more than one NAICS code to a single establishment, the U.S. Census Bureau (who produces the CPS data) does not–they assign a singular code based on the primary activity. As a quick aside, CPS doesn’t report NAICS codes, but rather Census industry codes derived from NAICS codes (though this seems slightly irrelevant for your question). Note that industry codes are assigned by Census Bureau employees based on employer name or the description provided by the respondent. You can read more about the methodology for the Industry & Occupation data in the CPS in this Census Bureau report.

Based on this information, I would assume that if two people employed by the same establishment gave the name of their employer, they would have the same industry code. However, if both provide only a description, there is a possibility that they may be assigned to different industries depending on the specificity of the description each person provides.