Yes. One must stop working upon the expiration of the EAD or the OPT. If an H1B petition requesting a change of status is filed prior to the expiration of the F-1 status (date of completing school or of finishing practical training, plus a 60-day grace period), one may legally remain in the U.S. However, one cannot work for the H1B-sponsoring employer during the period between the expiration of the practical training authorization and the start date on the H1B approval notice.