of the prospective employee. If employment with a single employer is desired for more than three years, it may, theoretically, be renewed indefinitely. Prior to October 16, 2008, the initial period of stay for a TN status holder was up to one year only. Renewal Renewal is accomplished either by an Extension of Stay mail-in renewal within the United States, requested as part of the employer's Form I-129 petition on behalf of the prospective employee, or by replicating the first-time route (TN status directly at the border for Canadian citizens; a new TN visa for Mexican citizens at a U.S. consular post and admission at the border). While TN status theoretically may be renewed indefinitely in three-year increments, it is not a permanent visa and if U.S. immigration officials suspect it is being used as a de facto green card, and with foreign residence abandoned, then they may elect to deny further renewals. The set of occupations permitted to petition for TN status is also quite a bit more limited than for the H-1B visa. Renewal is possible, in theory, indefinitely, but the TN status is not a substitute for permanent residency (a green card), and the border official has the discretion to refuse further renewals if she feels the ability for indefinite renewal is being abused. How this happens in practice depends largely on the mood of the individual border official. Some Canadians have successfully renewed TN status for a decade or more; others have found that after 3–4 years a border official may deny renewal. Dependents The spouse and dependent children under the age of 21 of a TN professional may apply for TD status (TD-1 for the family members of a Canadian citizen worker, or TD-2 for those of a Mexican worker). TD status can't be granted for longer than the period of time granted to the principal TN professional holder. TD status does not allow them to work, although they are permitted to attend school. In most states, non-resident tuition rates will apply for post-secondary institutions. If the spouse or child requesting TD status is not a Canadian citizen, he or she will usually still qualify for TD status, but must first request a formal TD visa at a U.S. consulate. The U.S. consulates reported 3,000 to 4,000 TD visas issued in each U.S. fiscal year from 2007 to 2009; this included visas issued both to