If it's the law, I like for someone to point me to it. I've never seen this in Mexican Law. (It does appear in U.S. Law, and I suspect that fact may lead people to believe there is such a rule, here, too.) However, I always leave open the possibility that such a law exists and I just have never seen it. (Anyone who can, please enlighten me by quoting the law on this forum, if you don't mind, copied and pasted directly from the text of the law, with a reference that will allow me to find it). I think the main issue facing an employer who is not at, or has already exceeded, the 10% of work force rule is whether the foreigner has the qualifications for the job he is being proposed to perform. Then, there are those who have no particular paper qualifications: I'm under the distinct impression that some percentage of foreigners who are working here, even working openly here, simply do not have permission to work. Others, with close contact with the service/tourism industries, will have a better read on this phenomenon, and may be in a position to comment. I think I see this often at Isla Mujeres, and it may also occur in the hotel zone with some regularity.
Yup, I know several foreigners here who work pretty openly without the proper paperwork. **As far as I've seen**, there doesn't seem to be anybody who checks up on this kind of thing.
Early December (2012) two individuals from Italy were deported by working illegally in one of the restaurants in Playa.
They probably antagonized someone, who then reported them to INM. I doubt INM puts too much time into random document checks, but those who work in tourism would know more about it. Waiters are the obvious ones: what about those manning phones, whom no one ever even sees? It would be easy to employ undocumented workers in some types of activities, with little or no risk of being detected. I personally know someone who's worked for years in an office, goes to work everyday in fact, and has never bothered to get permission to work here.
A U.S. man, an annual visitor to Puerto Morelos was on the beach last winter talking to me when 2 uniformed INM guys pulled him aside asking for his passport. It turns out that they seeking a guy who fit his description (59-60, long, white/blonde hair, tall) and the guy they were seeking was working illegally. Brent-Allen and they got into quite a debate over the issue and the fact that his passport was a mile away at his condo. Twenty minutes of back-and-forth later they left him alone. He never has worked a day in Mexico in his life - but he may have been a victim of a recently jilted PM woman, and hell hath no fury like it.
Immigration on occasions do spot checks on companies within the tourism industry and timeshare- I have a good friend who spent 4 hours hiding in a toilet during a raid. Working illegally is just not worth- piss one person off who suspects your status and immigration follow up on all tip offs.