This has happened today at the DNC rules committee hearing and is ongoing. They locked Bernie supporters out of the meeting and now they have been thrown out of the building. There were some Hillary supporters outside the room but it was obviously mostly Bernie people. The convention has not even started, Bernie Sanders was denied a permit to have a rally and we just got the release of the DNC emails documenting how the DNC was only for Hillary and used every resource to get her to win the primary. Those resources as we know were election rigging, use of the corporate owned news media, the spreading of misinformation and even money laundering through the state Democratic Parties.
From The Real News Network and they have more on YouTube.
This happened before.
They voted to keep superdelegates. CommonDreams has a really good article on this with some videos written by Jon Queally.