from immigration-law.com --> " one has to understand the rule of the employment-based preference immigration petitions. The rule is analogous to a "watershed" or "downhill water stream." For instance, once he/she obtains a "upstream" labor certification application such as EB-2, he/she is also eligible for "downstream" immigrant petitions such as EB-3. Accordinly, in this illustration, if he/she obtains a labor certification approval for EB-2 job, he/she can file two I-140 petitions simultaneously or sequentially, one for EB-2 I-140 petition and the other for EB-3 I-140 petition. If he/she chooses to do that, he/she can also file just a EB-3 petition using the certified EB-2 labor certification application. The same is not allowed from downstream labor certification application to upper stream preference immigrant petitions. For instance, if he/she obtained a labor certification for EB-3, he/she cannot file a EB-2 petition."