Courtesy of James K., Virtually Green, San Francisco, CA
In most states in the USA it's illegal for a for-profit farm to utilize volunteers, or interns, to handle routine farm work tasks that would ordinarily be done by paid workers. Many small organic farms have been using farm work volunteers and interns for years and gotten away with it but in recent years the Fed and state labor enforcement organizations have been cracking down and levying huge fines on farms violating the law. Here in California most small organic farms have stopped using volunteers and interns, which has hit many of them hard financially: some were heavily dependent on using such volunteers/interns to keep their labor costs down and be profitable.
Here's a link to an article in CivilEats, entitled "The Farm Intern Conundrum", that discusses the issue: https://civileats.com/2010/05/11/the-farm-intern-conundrum/
Sustainable Economies Law Center (SELC) has a section devoted to urban ag law, appropriately called UrbanAgLaw.Org. (FYI: I'm on the Advisory Board for SELC.)
Here's a link to a section of the website that specifically discusses the law in California related to urban (same for rural) farm use of volunteers and interns:
Discreetly check the laws in your state or province: being levied a $40,000 fine for labor law violations due to improper use of volunteers or interns can ruin your whole day.
Washington state a few years ago passed legislation that enables for-profit small farms to utilize interns if their farm gross sales are under $250,000 a year, but even there the farms must adhere to strict guidelines on the intern use. Efforts are underway in some USA states to pass similar legislation.