1. Can I begin working for new emp once I have filed H1B petition?
It depends. If you were previously on H1B status, then you are legally allowed to start working for the employer upon filing the H1B Petition. Otherwise not. Prior to the law signed on October 17, 2000, referred to as the American Competitiveness in the Twenty-First Century Act (ACTA), the INS has consistently taken the position that a person cannot start working for the new employer until s/he has approved the H1B petition.
If you are in the U.S. and the H1B petition is approved as a change of employer (with I-94 card updated at the bottom of the approval notice), then you may start working for the new employer upon filing the H1B Petition. If the H1B Petition is approved without an I-94, which means that the INS did not approve either the change of status or the extension of status but only approved the H1B petition, then you must first exit the U.S., apply for the H1B visa stamp at the home country consulate, and finally be readmitted on H1B status before starting the job.
