Is it legal for a restaurant to make their servers claim that they made a certain percentage of their cash sales?

I am a hostess at a well known Neighborhood Bar and Grill. Our particular restaurant was recently bought by a different company (we are a franchise). Before we were bought the servers and bartenders claimed whatever they wanted. Now they are being told they have to claim 15% of their cash sales or they will be written up or worse. This is causing a major drop in morale, as if restaurant jobs aren't stressful enough, because in some cases they are having to claim they made more than they really did. A lot of them are losing their food stamps and things of the like. Which brings me to my question. Is it legal for a company to "make" their employees do this?