Not sure what category to put this in but what are the rules regarding working in the States without a visa? Should I wish to report someone who is doing this what are my options and will anything be done? Thanks if you can shed light on the matter
You can't work in the USA without a (work) visa - not with a UK passport anyway. If they are found out they will have whatever visa they have cancelled, they will be deported and barred from applying for a visa for a number of years.
If you really want to shop them the Department of Immigration in the state they are in is probably the best place. Whether and how quickly they will do anything is another matter.