If the OP is in the US: in the US, 'labor law' and 'employment law' are two different specialties. Labor law focuses on the laws concerning unions, organized labor, and collective bargaining, while employment law is concerned with laws affecting all aspects of the employer-employee relationship. You'd want an employment law specialist for this sort of issue, or a generalist lawyer with experience in helping software engineers deal with employment law issues.

Asking for a labor Lawyer won't get you anywhere, but smutticus is right that reaching out to Unions or Labor Lawyers and asking for an employment lawyer is a smart move.

Big Unions often employ or know top notch employment lawyers (it's not a focus for unions, but they still might work together on select cases), employment lawyers that can scare the acquiring company before negotiations begin :p