Whether you're writing for charity or profit, your writing is still YOUR WRITING and nobody can publish it without your permission.

When this happens, you should send the company an invoice for unauthorized use of your work. If they don't pay, contact their ISP. You can find this information by typing in their domain name at: http://dns411.com/ (leave out the http://www. part of it).

I don't know what your contract is with your contributors but please understand that the person who owns the rights to the writing is who should approach the copyright infringer.