I actually described the issue in question on HN in the past which promptly led to Uber threatening the employee who leaked the details to me. He was so scared that he asked me to reach out to YC and have the original post deleted.
I wouldn't hesitate to share the evidence with a journalist with a publication backing them though as that would be a more appropriate venue.
Have you reached out to anyone? https://www.nytimes.com/newsgraphics/2016/news-tips/ would be my first place to go. It even specifically calls out "Here is proof that this company is conducting itself unethically" as an example, and asks for evidence corroborating the story. So if you have it, that would seem to be the place.
Having said that, I was more wondering if the people doing the threatening could be turned to better use. They surely aren't in it for the warm fuzzies, and if they're good at digging perhaps they could be convinced to do it for the good guys.
I wouldn't hesitate to share the evidence with a journalist with a publication backing them though as that would be a more appropriate venue.