If Uber had 'picket-lined' a location (like JFK) against all pick-ups for a time period, that level of driver control could work against the preferred independent-contractor characterization of their driver-relationships. Whether the employer dictates the exact places, times, and manner of service is a part of that evaluation.

It also seems odd to have an employer dictate to its contractors (or even wage employees) to participate in a labor action, or political protest.

Shouldn't that be the workers' decision? Uber didn't force anyone to either do, or not do, JFK pickups.