Not cops, but....
My wife (Filipino) was an OFW in Korea when I met her while I was serving in the Army. Her contract ended and I followed her to the Philippines so we could get married. The agency that she worked for refused to give back her passport (which I needed in order to proceed with her a VISA to the U.S.). They claimed that she had another year left on her contract (she wasn't aware of this), and that we'd have to pay a large sum of money in order to get it back. We left Manila that day, disheartened.
Luckily I was able to research the company and I found the CEO's email address. I emailed him, explaining how this was essentially slavery, and that I would report them to the proper officials if they did not relinquish her passport.
I know that it is illegal to keep someone's passport, but I doubt that I had the capacity to pursue any legal action within the limited amount of time that I had left over there. Luckily, the term "slavery" must have scared the heck out of him, as they called me within a day of the email, offering to release her passport without any penalty.