Both @IamSoNotListening and @shoover have provided great answers from a Federal perspective but it is important to remember that in the United States laws are also designated at the state and local level as well.
OSHA and ADA lay out general outlines for requirements of businesses (and are a good start) but I think you may be looking for something more specific that will only be found in your local building codes for commercial zoning.
These will largely be state and municipality dependent so you'll have to search online (or talk to a general contractor) to get the rules for your area (key search words being: city, building code, zoning laws). Typically codes will be divided by specialty (such as electric code, plumbing code, fire codes, etc..). Also typically there will be separate codes depending on the type of zoning you are working with (single family home residential, multiple family home residential, commercial, industrial, etc..)
So for example, if your business is in the city of Denver, Colorado you would refer to this Denver Build Codes, Policies and Guidelines link. Other cities, states, and municipalities will have their own version of this information. Worst case scenario - if you live in a very small town - you may need to go down to your local courthouse in order to get a hold of these laws. In that case, I might recommend talking to a lawyer or professional builder who is familiar with the codes.
Lastly, you asked about enforcement... OSHA has it's own enforcement policies but there are also state employed building inspectors who are usually required to sign-off on any new building or major renovations. These same departments will also field complaints about building compliance. Just keep in mind that many older buildings are grandfathered into less stringent rules until they make a major renovation so at the end of the day you might be better served chatting with one of these building inspectors before you file any official complaints.