If I contribute code to an open source project under the BSD 2-Clause license and don't sign any contributor license agreement, can the maintainer relicense the code without getting my permission?
Sure, anyone can do anything. It would be up to you (and hopefully a lawyer) to then sue them and let judge/jury decide. Or, convince authorities that some criminal law was violated and they should investigate.
Both of which are hard and/or expensive. So most rely on public shame. Out them on social media and foment outrage.