you should ask your EMPLOYER write a letter for you to confirm that you are still hired, and donot forget bring 2-3 latest pay check(stubs)with you, and I'll give you two links as follow, print out, bring that with you always, just in case. good luck!
http://www.washingtonwatchdog.org/documents/cfr/title22/part41.html
http://uscis.gov/lpBin/lpext.dll/inserts/22cfr/22cfr-1/22cfr-713/22cfr-1339?f=templates&fn=document-frame.htm