Three different concepts control a foreign national's authorization to remain temporarily in the United States: (1) I-94 expiration date, (2) visa expiration date, and (3) petition expiration date. Each of these documents may expire at a different time than the others and each confers a different right.
Some types of status require an employer to serve as the petitioner, like employment-based temporary status including H-1B, L-1, E-1, E-2, P-3, O-1 and others. In these sorts of cases the petitioner files a petition with USCIS and USCIS approves it on Form I-797, which is printed on a multicolor letter-sized sheet of cotton bond paper. Applicants for some status like B-1, B-2, and TN do not require a petitioner, and so there is no "petition expiration date."
These three different documents have overlapping control and a foreign national must use care in determining when his status expires:
A foreign national can only have status while inside of the United States. Status is the name of the permission CBP, or USCIS gives to the foreign national to remain in the United States. A foreign national outside of the United States does not have status. A foreign national inside of the United States who has entered without inspection, or overstayed an authorized period of stay is said to be "out of status."
The document that controls the foreign national's status may be the I-94 card, or the I-797 approval notice (if for a change of status, or extension of status). The document that controls is the one most recently issued. This is an important concept to understand. If you have an H-1B I-797 extension of status approval notice valid until December 10, 2012 and you leave the United States and reenter and at the port of entry, the Customs and Border Protection Officer issues you an H-1B I-94 card valid until May 1, 2012, your status expires on May 1, 2012 and not on December 10, 2012. If you mistakenly remain in the United States until December 10, 2012, you will have accrued unlawful presence for more than six months and be required to remain outside of the United States for three years.
Reciprocity is the State Department's rule that if a foreign country allows US citizens more limited rights under a visa program, the US State Department will offer that country's nationals the same treatment under US immigration law. So if China issues US workers a one year work visa and the most closely related US visa is the three year H-1B, the State Department will restrict Chinese nationals to the same period for their H-1B visas.
In the case of H-1B and some other visas, the Consulate is supposed to issue the visa valid until the I-797 petition expiration date, unless reciprocity requires that it be issued for a lesser period. Appendix C, Volume 9, Foreign Affairs Manual (or the visa is restricted under section 212(d)(3)). When the consulate must restrict the visa to a shorter period, the consular officer should note below the visa stamp: “Petition valid to [date].” Most visas now have a note "PED" followed by a date where PED stands for "Petition Expiration Date."
Subject only to the passport requirement of section 212(a)(26) of the Act or any limitation on the period of admission noted on the visa page as the result of a section 212(d)(3) order, an immigration officer shall admit the beneficiary, if admissible, to the date until which the petition is valid or, in the circumstances previously indicated, the date until which his or her temporary stay has been authorized. O.I. 214.2(h)(9).
The State Department guidelines make this point repeatedly. See, e.g., 22 CFR 41.112(a) (“The period of visa validity has no relation to the period of time the immigration authorities at a port of entry may authorize the alien to stay in the United States”); 9 Foreign Affairs Manual, note 3.5 to 22 CFR 41.112 (“The validity of a visa relates solely to when the visa may be presented to an immigration officer at a port of entry. It has nothing to do with the period for which that official may admit the bearer of the visa. For example, a B-2 visa holder whose visa may expire a week after entry could nevertheless be admitted for 6 months or 1 year, the latter being the maximum initial period of admission allowed under INS regulations”).
When the consulate must issue an H or L visa with a validity period shorter than the petition,“an immigration officer shall admit the beneficiary, if admissible, to the date until which the petition is valid.” See INS Operations Instruction 214.2(h)(1). See also letter from Lawrence J. Weinig, INS Deputy Assistant Commissioner for Adjudications, regarding INS policy when an alien has an approved L visa petition and L visa with differing dates, reproduced in Interpreter Releases, Vol. 66, No. 36, September 18, 1989, pp. 1033, 1046-1048.
The passport of an alien applying for admission must be valid for a minimum of six months from the expiration date of the contemplated period of stay, unless otherwise provided in this chapter.
8 CFR 214.1(a)(3)
The passport of an alien applying for extension of stay must be valid at the time of application for extension, unless otherwise provided in this chapter, and the alien must agree to maintain the validity of his or her passport.
8 CFR 214.1(a)(3)