When someone uses the phrase "biological attack" your mind doesn't immediately leap to hippy cults, but the biggest attack of this kind in US history was conducted by a free-love preaching sect.
In the 1970s, Bhagwan Shree Rajneesh became the leader of the (modestly named) Rajneeshees, in his home country of India. The cult's attitude towards sexuality (as well as a massive unpaid tax bill) put them at odds with the conservative (and tax-demanding) Indian government. So, in the early 1980s, a large group of the Rajneeshees fled to set up life in the US.
They settled on a 64,000-hectare ranch in central Oregon, planning to turn it into a bonafide city. The problem was that the leaders of the cult had failed to read the small print when purchasing their land. Though they owned the land, they couldn't just build whatever they wanted on it, nor move in as many people as they choose – they would need permission from the local authorities. This was a little bit of a problem, given that the leaders of the cult did not exactly mesh well with the locals.
When attempts at diplomacy with the local Wasco County authorities failed, they turned to more aggressive tactics to get their own way. Their first move involved overwhelming the vote in the nearby town of Antelope, which only had 50 residents. This allowed them powers such as being able to have their own police force – as well as some powers that were incredibly irritating to the local residents. They renamed the town "Rajneesh", for instance, while to the local recycling center they bestowed the moniker the "Adolf Hitler Recycling Center".