Yes it is illegal. You can only work for the approved H1B petitioner(s) whether for a single one or concurrent employer.
The way you want to see this is - will any reasonable person do this work without expectation of remuneration if you were to hired them? If no one will hired to do it for free, so you will not be expected to do it without being paid, whether you are actually getting paid or not is irrelevant.
This response is general in nature and cannot be construed as legal advice, given that not enough facts are known. If you wish to discuss your case further, you may seek an appointment here - www.lawyersharma.com/book-online.
It is illegal to work in your startup pondering an idea while on an h1b visa is ok.
Is my answer "BEST ANSWER" and/or "HELPFUL"? If so, please acknowledge and mark it so. Mr. Smith has 25 years of successful U.S. immigration law experience with cases just like yours. Still, his response is general in nature, as all the facts are unknown to him, and cannot be construed as legal advice. Please retain immigration counsel to analyze your particular situation in order to receive specific advice. Specific answers requires knowledge of all the pertinent facts of your case. Any answers offered by Mr. Smith on Avvo are of a general nature only, and does not create an attorney-client relationship.
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