Can I be terminating for having a flash drive connected to my work PC

What do your civil service papers say? Employee handbook, collective bargaining agreement, performance evaluations over 5 years, any and all verbal or written disciplinary notices over 5 years, promotions, etc... make sure you obtain a complete copy of your personnel file. It is subject to FOIL so anyone could obtain it if they paid for copies.   What does your union recommend? You need to exhaust all of your administrative remedies. If you face an adverse employment action which is sustained make sure to timely appeal that. Retaining private lawyers will be expensive so cooperating with union counsel might be a good idea.   If none of the above work are you being discriminatorily targeted? None of your facts reflect that. Consult with employment lawyers for possible discrimination although data security breaches if you should have known sound potentially serious. Especially if you deal with CONFIDENTIAL data that sounds compromising or potentially compromising.   We live in strained times. Data breaches can be catastrophic and the state or local governments have serious duties to protect breaches or even potential breaches. You have your work cut out for you. If you dont work as hard as your union or private counsel does to save your career it might be short lived.  Good luck.