Giving Lectures while in H-1B Status
On the basis of the H-1B petition Virginia Tech filed on your behalf, you may only work for Virginia Tech and only in the position for which the position was filed. To work for any other employer, the other employer must file an H-1B petition on your behalf.
Please note that the negative consequences of working for an employer without the proper authorization, i.e. H-1B petition on file with USCIS, are significant: if you worked without the proper authorization, you are considered out of status and may not work for Virginia Tech. You may also be required to leave the US to obtain a new H-1B visa sticker and to re-enter the US before you could resume your activities at the university. Employment without the proper authorization may also make you ineligible for certain future immigration benefits.
It is acceptable to participate in outside lectures without a concurrent H-1B petition, but you may not be paid for such activities (unless the employer filed a formal H-1B petition on your behalf.) You may, however, be reimbursed for your travel expenses.