To "NSL" someone means to evict, kick out, exclude, arrest, or eliminate them because they violated an ill defined law - but in reality their real crime is to say something the bosses/
higher-ups don't like.
It's based on the Hong Kong "
National Security Law", which is used in a subjective and arbitrary to arrest, detain, harass, or
impression anyone who disagrees with the current government.
If someone you know got "NSL"ed, it means they were arrested for some benign, arbitrary, or made up crime when in reality what they did wrong was upset the people in charge.