If you are currently in the United States and need to travel internationally while your I-129 petition is pending, you should contact IFSS to make sure the trip does not adversely affect your petition.
Generally, if you are filing a change of status from another non-immigrant visa category, travel may result in USCIS approving your requested status, but denying the change of status portion of your petition. As a result, once your petition is approved, you will have to physically re-enter the U.S. in order to activate your status.
If you are filing an extension of stay or a change from one employer to another, you can travel if you have a valid status upon return and unexpired H-1B visa stamp in your passport. This is also typically the case even if your unexpired visa was issued under a previous employer’s name (NOTE: in early 2019, a few employees experienced difficulties with this--please consult IFSS to get an update and we will advise accordingly). If your H-1B visa stamp has expired and you travel while your H-1B extension is pending, then you will have to remain outside the United States until the extension is approved so that you may obtain your new visa stamp and re-enter the United States.