The following answer refers to the situation where the owner of the business is Jewish. Several other permutations exist, but they are beyond our present scope.[1]
The gemara[2] says that, in order for a structure to be obligated in having a mezuza, its use must have some connection to that of a dira (dwelling). However, it is not always simple to determine what uses meet this criterion.
The Rambam[3] says that a store in a market is not obligated to have a mezuza. It is, therefore, surprising that he rules that storage rooms used for straw or lumber are required to have a mezuza. The Taz[4] explains that storage rooms must have a mezuza since they are used both in the day and at night. Stores, however, are exempt from having a mezuza since the commercial activities of a store are limited to the daytime. Other distinctions can be made. For example, in contrast to a store, a storage room is used as an extension of one’s home, which makes it more “dira-like.”[5]
Along the lines of the Taz’s distinction, the Pitchei Teshuva[6] cites the opinion of the Yad HaKetana, who states that if the store houses the owner’s merchandise during the night as well, then it would certainly require a mezuza. Even if one does not agree with the Yad HaKetana, if the business or factory operates well into the night, it is more probable that a mezuza would be required.[7]
A further reason to obligate having a mezuza is the approach of the Bach,[8] Perisha,[9] and Yad HaKetana,[10] according to whom, the Rambam (and, likely, the Shulchan Aruch) was misunderstood in his ruling regarding a store. The Rambam,[11] in the aforementioned passage, rules that a sukka and living quarters on a ship are not obligated to have a mezuza because they are not permanent dwellings. Considering this, the Rambam could be understood to be referring specifically to a store that was part of a market that was open only on special market days. This was a common arrangement in the gemara’s time.[12] Accordingly, regular, full-time places of work would be obligated to have a mezuza.
In summary, there is ample justification to affix a mezuza in places of work. Regarding a beracha, several recent poskim recommend a safe approach: it is better not to make a beracha because of the doubt in the matter.[13] Yet, we recall that our mentor, Rav Yisraeli, instructed us to make a beracha when affixing the mezuza to the doorpost of our office. Still, we cannot say with certainty whether this was a blanket ruling or it depended on the type of activity and the conditions of the specific case.