PRIVATE LOTS
When a parking lot is reserved for customers and you’re not exclusively dealing with the proprietor’s business, it’s unlawful to park there, even for only a few minutes. You can be towed, and you’ll have to pay for the tow if you can’t produce a receipt from the business from the period when you used its lot.
http://www.nyc.gov/html/dca/html/publications/publications_towing.shtml