You can read the full story here, including a statement from the restaurant:
Apparently, after a diner posted a comment about a waitress drinking from her cockail at the table (with a humorous, and not hostile tone, I might add) PS7, when unable to coax a confession from any of the waitresses on staff that night, fired all four female servers who worked that night.
I find that kind of scorched earth policy to be particularly appalling in this economy, and also in violation of Title VII anti-discrimination on the basis of sex. If the diner had reported that an Asian server had done the same, and there were four Asian servers on staff, would PS7 have fired them all based on their race? It's no different for sex.
The waitresses were offered their jobs back (probably after consulting with their lawyer) but all but one refused. I can't say I blame them, and I will not be dining at this restaurant.