taste of Asian undocumeted add on charges- mandatory 20% gratuity on dining service gainesville, Virginia

upon finishing dining, and waiting a ridiculous long time for the table to be cleared, the check was presented with a 20% Gratuity charge for a party of 4 (2 adults, 2 children), the manager insisted it was their right, although she was unable to show where it was listed in the menu. The service was terrible and worthy of 10% tops. only a threat to call the police on site caused her to remove the charge. very ugly situation. There is no justification to add a 20% gratuity charge for a table of 4 without it being listed in the menu of charges, or without any other posted notice in the premises.Since it is located across the street from a senior center one can only make an assumption about the predatory charges and the target group who would pay without challenge.