working on two jobs using two H1bs. Neither of the employer know but both have h1b approved. can i work for both.?

Having two H-1B's is not the same as having two different nonimmigrant statuses in the US. My guess is that you can work legally for two H-1B employers as long as you have approvals for both as long as you are maintaining the working conditions as specified under the H1B petitions. I do not believe that checking a box for concurrent employment is the determinative factor in whether an additional H-1B employment is valid. Due to the limitations of the Lawyers.com Forums, Alan Lee, Esq.'s (the "Firm") participation in responding to questions posted herein does not constitute legal advice, nor legal representation of the person or entity posting a question. No Attorney/Client relationship is or shall be construed to be created hereby. The information provided herein by the Firm is general, and requires that the poster obtain specific legal advice from an attorney. The poster shall not rely upon the information provided herein as legal advice nor as the basis for making any decisions of legal consequence.