That's the claim being made by this eyewitness:
She described a November 14 incident where helicopters were encircling protesters at night with no lights on. She says from 1:40 to 2:20 am, an aircraft was circling the encampment. Then, at 5:30 am an aircraft was observed that looked like a crop duster: she described 2 hoses under each wing and suspects they were spraying some kind of chemical or bacterial agent on them.
You can read the rest @
By the way, there is persuasive evidence that police "protecting" Bill Clinton used a nerve agent against US citizens in 1999. You can read about it here:
Why are we whining so loudly about CW agents in Syria when our own government is using them against us? Let's get our priorities straight, people.