An employer cannot require you to volunteer and work unpaid hours unless it falls under your job description. If the volunteering is presented with the threat of adverse employment action if you do not comply, then you may have a claim for unpaid wages.
Volunteers' rights You do not have a contract of employment as a volunteer, so you do not have the same rights as an employee or worker. You will usually be given a volunteer agreement that explains: the level of supervision and support you'll get. what training you'll get.
Depending on your country of citizenship, you may need a visa to volunteer in the US. Check with your local American embassy to learn about the requirements for your country. Be a responsible volunteer abroad and put the community first.
In general, it's not possible for foreigners to apply for jobs in the United States without having the appropriate work authorization, which typically includes a valid work visa or authorization to work in the country.