Parties to a coract are always free to rengotiate their contract, and that's largely true of lawyers and their clients.
Clients are always able to fire their lawyer, for any reason. Lawyers have less freedowm, and have a lot of latitude in who they represent, but state ethical rules prevent certain thigns, and one of those things is dumping a client when the timing prejudices their case. If the timing doesn't prejudice the client, then lawyers aren't forced to represent anyone. It's also not all that common for business litigation to be on a contingency basis rather than hourly, since the liabiity isn't a slam dunk like it iften is in the case of personal injury cases.
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This is an issue contract and ethics. It has nothing to do with civil liberties.
So you are saying you signed an agreement and six months into the attorney wants to change the terms? Then, because you did not agree to the new terms, he decided to withdraw from the representation? If so, the attorney may have violated various contract and ethical duties.
If you have a contingency agreement the attorney can only withdraw under the terms of that agreement. So was the withdrawal allowed under the terms of the agreement or not? If not, he cannot just "fire" a client because the client refuses to agree to new terms.
Provide more facts because your post is not entirely clear.
This answer is for informational purposes only and is not legal advice regarding your question and does not establish an attorney-client relationship.