Begin by consulting with an employment and or labor law attorney. This is not an immigration law question.
Kindly be advised that the answer above is only general in nature cannot be construed as legal advice, given that not enough facts are known. It is your responsibility to retain a lawyer to analyze the facts specific to your particular situation in order to give you specific advice. Specific answers will require cognizance of all pertinent facts about your case. Any answers offered on Avvo are of a general nature only, and are not meant to create an attorney-client relationship.
Employer is obligated to pay you higher of Prevailing Wage (listed in LCA" or Actual Wage. Nothing more. Nothing less. Under H-1B regs, end-client is not your employer. H-1B petitioner is your employer and responsible for payment/employment incidents. To access your claim for back wages, please proceed through an attorney.
H1b employer is required to pay prevailing wage or actual wage. Your question is not an immigration question but rather a question for an employment labor law atty.
Attorney Robert Brown's (former INS Director, 1972-99) reply to your question is general in nature, and does not constitute legal advice as all facts are known to him. For specific advice or representation you should retain an attorney experienced in immigration law. Mr. Brown's reply on AVVO does not create an attorney/client relationship not constitute legal advice.
A meeting with a state licensed labor attorney is the most necessary logical step to take.
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