The United Private Hire Drivers (UPHD) union which last month disrupted Westminster with protests, staged the demo at Heron Tower over the firm's use of the corporate Uber for Business service, with between 25 and 30 protesters making their voices heard.
And the group said it plans to target more businesses with ties to the startup in future.
The drivers also held an earlier protest at City Hall where London mayor Sadiq Khan was holding Mayor's Question Time on Wednesday morning.
The minicab drivers are calling on Khan to include worker rights in Uber's license to operate in the capital. It is also making a stand against the introduction of mandatory English tests for drivers which is claims are discriminatory.
Drivers were handed support in the row after Labour MP and chair of the Work and Pensions Committee Frank Field said Uber treated drivers like "Victorian sweated labour".
He backed calls for working practices to be part of Uber's conditions of license which is up for renewal next year.
And while Farrar said drivers felt government was starting yo listen to their concerns, a lack of action from Transport for London and the mayor meant it would be seeking to reach consumers directly by targeting businesses using Uber services.