FYI, check out the last line!

Do I need a visa to work in Mexico?
Yes, Americans who wish to work in Mexico must have employment visas. For more information, contact the Mexican Embassy or Consulate nearest you in the United States. The Mexican Embassy maintains a list of the addresses of its Embassy and Consulates in the United States. You may also wish to contact the Mexican Immigration Office, Homero 1832, Col. Los Morales, Mexico, D.F. Telephone: 011-52-5-387-2400. [b](You should expect that the person who answers your call will speak only Spanish.) [/b]
http://www.usembassy-mexico.gov/eACSfaq.html