[ Tell them to go get the police and start eating.
When the police arrive, ask them if they have a search warrant and accuse the government worker of trespassing, assault, battery, extortion, whatever. Tell them that every person in this party will need to be arrested and taken downtown and refuse to leave. Then they will file a complaint and call their local news outlet.
Continue eating until they bring the search warrant (they won’t) and when finished, offer the government worker a toothpick. ]
Even better if the county Sheriff is like Joe Arpiao invite him and have him come to it, then when the health dept. comes he can arrest them for trespassing ininvited on private property.
Imagine what a sympahetic Hollywood could do with your scenario. :-)