I'm an engineer with a technical job in the pharmaceutical industry. However, I really want to work as an engineer at a large corporation that produces chocolate and confectionery products. I have some relevant training and plenty of transferable skills, but no direct experience in the food or confectionery industry.
I am currently working with a career advisor who suggested that I should volunteer at the particular companies that I'm interested in, with the goal of getting hired for a paid position. I have no problem with volunteering to gain experience. However, I'm concerned that I will come off as desperate by asking for an unpaid technical position at a large, for-profit corporation. It's a different story if internships are available, but I rarely meet the criteria because I've been out of university for a few years. I would think that there are also legal issues, trust issues (who wants to reveal the trade secrets to a volunteer?), never mind that most for-profit companies aren't set up for volunteers. At the same time, it seems like it would be a good opportunity for me to gain experience and visibility. Do you think it's worthwhile (or even possible) to approach a company for an unpaid technical position?
There are so many issues here -- starting with the fact that your career advisor might be full of crap. I don't have enough details to say with confidence, but I'm questioning her assertion that you need experience in the food or confectionery industry to work as an engineer in it. (Any engineers want to back me up or refute me?)
But to your direct question, yes, there are problems with volunteering for a for-profit corporation. With the exception of nonprofits, the Department of Labor requires that unpaid work be primarily for the benefit of the volunteer, not the employer. And if it's not, they can reclassify you as an employee and require the employer to pay back wages for all the work you did.
Now, do companies violate this rule all the time? Yes. (Although the Department of Labor is supposedly cracking down on it.) But a smart company or a company with an alert HR or legal department isn't going to mess with this.
I think you'd be far better off making contacts at this (delicious-sounding) confectionery company you want to work at and seeing what their advice is for you. And I am going to view your career advisor with great skepticism until/unless someone corrects me.